All eyes were on Real Mallorca versus Unión Deportiva Levante. Now there's a line you don't read often. Mallorca and Levante, after all, have among the lowest attendances in La Liga and rarely interest anyone else until the big two bring their travelling circus to town. Mallorca are bottom. Levante have been one of the great success stories recently, surviving and winning, heading into Europe for the first time, but they've collapsed so badly as to become 2013's second-worst side. Like Mallorca, they were never the prettiest team anyway: these two average little more than a goal a game and it was one of them – and possibly both – that a Spanish Federation official referred to when he confided that a pay-per-view game had been bought by 47 people.

As if all that was not enough, it was going out at midday on Sunday – not as bad as Monday at 10pm but not the most popular slot. Yet this time was different. This time, they were watching and closer than ever: every move was scrutinised, every gesture analysed, every action pored over, seeking a clue, a sign. Something to confirm their suspicions or to put their minds at rest. The reason was the return of the depressingly familiar talking point of the final weeks in Spain, when teams with nothing to play for face teams with rather a lot to play for: the maletín or little suitcase. Third-party payments, in other words. Or, to put it another way, match-fixing.

A distinction is normally drawn between third-party payments given to sides with nothing else to play for as an incentive to win – as if that's fine and dandy and doesn't raise all sorts of awkward moral, practical and legal questions – and third-party payments given to teams to lose, which are assumed to happen less frequently. More importantly, nothing ever happens and no one ever seems to really care. Every year, as the season enters its final weeks, there are a series of results that would be astounding if they weren't so predictable and yet the whole thing is treated as just an inescapable, if unfortunate, fact of life.

Spoken about with a lightness and a "normality" that can be startling, everyone seems to accept it as true but no evidence is ever presented and no investigation ever launched. Even when there have been recordings, the story has exploded into life one day and disappeared the next. No outrage, no punishment. Until now?

It all started on 13 April. Levante, theoretically safe having reached 40 points, were playing Deportivo de La Coruña at home. They had nothing much to play for, officially at least. By half time they were already 3-0 down and the midfielder Barkero was furious. He turned on his team-mates and accused them of not trying. It started with the goalkeeper Gustavo Munúa, then Sergio Ballesteros became involved, then Juanfran. Barkero accused them of being bought and they almost came to blows. Barkero insisted that he wanted no part of the pantomime and subsequently told the president that he no longer wanted to renew his contract: he would leave in the summer.

During the argument the manager and the president had to intervene, the former calling for a team meeting on the Monday, during which the accusation was repeated. But, when challenged, Barkero admitted that he did not have concrete proof for such grave accusations. Yet against Celta Vigo, it was Munúa and Ballesteros who were left out of the squad, while Barkero was still in. Levante were dreadful, barely breaking into a sprint, barely making a challenge. They lost 1-0. And here's the twist: Barkero missed a penalty.

When the story of the dressing-room confrontation broke last week, no one at Levante denied it. Barkero gave a press conference in which, instead of rubbishing the media's stories, he rubbished his own, albeit half-heartedly. He apologised to his team-mates for making an "erroneous" accusation.

For Deportivo, the side that eventually beat Levante 4-0 and who now felt the finger of blame pointing their way, that was not enough. The president Augusto César Lendoiro was spitting blood, demanding an apology from Barkero, even though he had never made any public accusation. Lendoiro and the club's captain, Manuel Pablo, then made similar remarks that in a curious and rather sad kind of way summed up the attitude in Spain for years: they were furious at the accusation that their game was bought, but seemingly equally furious at the implicit suggestion that it might be the only one. Meanwhile, what better way to criticise an accusation without proof than by making another accusation without proof?

"Everyone knows that if there is a club that has behaved with total honour, it's Deportivo," Lendoiro said. "We're absolutely indignant. There were other cases, some of which cost us relegation, but as we did not have proof we kept our mouths shut. Cases where we knew what was going to happen and it happened." "You can be suspicious of Levante-Celta too," added Manuel Pablo. "There are always suspicions; it cannot just be focused on our match." Others suggested there is no way that Depor, bound up in administration, could afford to buy games. (Although it is of course teams in financial crisis that can least afford not to: relegation could mean liquidation.)

Levante, by contrast, acted with caution. The coach, Juan Ignacio Martínez, said he would put his "hand in the fire for the players' honesty". His players have performed fantastically in the last two years, based largely on commitment and seriousness, on togetherness and spirit, so it must be a particularly difficult accusation to face. But the club insisted that if there was anything suspicious they would act decisively against those responsible. Juanfran welcomed the investigation as a way of "cleaning things up as soon as possible". And the president, Quico Catalán, called it a "delicate situation" as well as admitting that he had spoken to the league's president, Javier Tebas, who had explained what was happening.

That was the difference. By then, they knew that something had shifted. They knew that this time the LFP was determined and had decided to investigate. Tebas, who took over last week, has said repeatedly that ending match-fixing is one of his priorities. The Levante-Deportivo game was already being monitored, the findings passed on to the anti-corruption prosecutor and a formal denuncia made by the league. Tebas had not intervened publicly during his long spell as vice president and de facto power at the league, although behind closed doors he did lean on clubs to take the issue more seriously. Now, in his first week as president, he had put a fist on the desk.

This time, it seems, there may be evidence, including recordings and text messages. This time it might actually become a criminal case – one in which players could face a two-to-five-year jail sentence and clubs could be docked points or kicked out entirely. In the past, that could winked at you, whispering: "Aye, could, but won't". This time, there is hope.

Because it could become a criminal case, few specific details have emerged. But Al Primer Toque, the nightly show on Onda Cero radio, reported that the sequence appears to have been Levante players contacting the striker Carlos Aranda at Granada and telling him that they had an offer from Depor (which need not necessarily be true, of course) to throw the game and did Granada want to make a counter offer for Levante to try and win it, thus aiding their survival bid? They would, in other words, auction their effort. According to this version of events, Aranda told Granada's president, Quique Pina, and he alerted the league. At which point the monitoring began.

When the story broke last week, it came into the open. Subject to an investigation, the full facts are unknown but the very fact this was now public brought consequences. Some perhaps unfair, some certainly beneficial. This weekend clubs found themselves being watched, and because of that things changed. Any step out of line would be considered suspicious. It was not enough just to be clean; teams had to look clean too.

A fundamental truth emerged: Levante have overachieved this season. They were safe with weeks to go and went on a Europa League run longer than anyone could have imagined; they have the oldest team in the league – Ballesteros is 37, Munúa 35, Juanfran 36 – and they have reached the end shattered, struggling to the line. This is not a team that can offer very much more physically. In the 27th minute, Barkero was withdrawn injured. If that looked like another layer of intrigue, it was a passing sensation.

By then, they had gone behind to a sixth-minute Tomer Hemed goal that would have given Mallorca three points every bit as vital as those gathered by Celta and Deportivo against Levante. But a Robert Acquafresca equaliser gave Levante a 1-1 draw, leaving Mallorca bottom, four points and goal difference away from safety. The point was Levante's first in five matches; it took them to 41 and gave them a little breathing space. Now all they can do is wait. "We came off the back of a difficult week because of everything that has been said about the 0-4 with Deportivo but the team found strength," Martínez said. "They demonstrated once again how hard they work once again and God willing Levante will emerge clean from the investigation. This draw honours the squad."

Talking points

• Et tu, Pepe? After José Mourinho's performance on Friday, Madrid were back at the Bernabéu on the Saturday, where the manager was whistled and booed and even the man assumed to be his most loyal player, appeared to turn on him. Pepe, obviously aware of the fact that Mourinho's days in Madrid are numbered while he may yet have years to come, described the coach's words as "not appropriate" and demanded more respect for Iker Casillas.

• And so Sevilla are back into a European place after beating Espanyol 3-0. The same Espanyol who have not won since they said they would try to get a European place. "Every time we mention Europe," said the coach Javier Aguirre, "we crap ourselves."

• So a banner that said simply "ResPEPct" got pulled down at the Camp Nou. Pathetic. Meanwhile, out on the pitch Leo Messi came on and scored twice – both of them brilliant – to turn it round and enable Barcelona to win 4-2 against Betis. Just when it was getting a tiny bit nervy too. Lose and Barcelona could have gone into their game at Atlético next weekend just two points ahead of Madrid. As it is, they may go into that match already champions.

• Zaragoza win again. Mind you, if ever there was a home banker that was it. They're back out of the relegation zone now, but it's very, very tight down there: Granada, who beat Málaga 1-0, are on 35 points, Zaragoza and Osasuna on 33, Depor 32, Celta 31 and Mallorca 29.

• Bye, bye, Sheik? It certainly looks that way, after the real reason that Al-Thani came to Málaga was finally snatched away from him – the chance to build the new port project.

Results Celta 1-1 Athletic, Valencia 4-0 Osasuna, Granada 1-0 Málaga, Real Madrid 4-3 Valladolid, Deportivo 0-0 Atlético, Mallorca 1- 1 Levante, Zaragoza 3-0 Rayo, Sevilla 3-0 Espanyol, Barcelona 4-2 Betis. Monday night: Getafe v Real Sociedad