Son Heung-min’s anguish at Everton on Sunday knew no bounds and it is no exaggeration to say that on Monday, as the guilt at his role in André Gomes’s horrific injury continued to consume him, the Tottenham forward could not even think about this Champions League test against Red Star Belgrade.

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Mauricio Pochettino and the Spurs dressing room closed ranks around him. They told him that in no logical world should his trip have led to such damage to Gomes’s ankle and they believed that the best medicine for Son was to get straight back into the saddle. There was no point in moping.

On a night when Spurs registered their first away win of the season, it was Son who provided the cutting edge. His sixth and seventh goals of the season in the second half allowed his team to coast to a victory that has put the last 16 of the competition within touching distance. For them, the equation is simple. If they can beat Olympiakos at home in three weeks’ time they will reach the knockout rounds for the third season in succession.

Spurs could temporarily forget their domestic woes as, not for the first time, the Champions League provided a tonic. Giovani Lo Celso, on his full debut for Spurs, scored the first goal, a moment that embellished a performance of no little slickness, and Christian Eriksen, who entered as a substitute, added a late fourth.

Pochettino could enjoy productivity from all three of his summer signings. Never mind Lo Celso, Tanguy Ndombele was excellent and even Ryan Sessegnon, who came off the bench, supplied the assist for Eriksen.

Red Star rued the squandering of two excellent first-half chances but Spurs simply had more quality. They hogged the ball, they led the shot count 17-5 and, at the end, there was the sight of Son and Pochettino offering their thanks to the travelling support.

Son’s goal celebrations were subdued. The first was a praying gesture and he revealed that it was his way of showing respect to Gomes. “I didn’t want to celebrate because I just want to respect the situation,” he said. “It’s been a really, really tough few days. I’m really sorry for the accident but I had to focus for the team. I want to wish André Gomes to get well soon.”

Facebook Twitter Pinterest Paulo Gazzaniga stretches out a left boot to deny Red Star’s Milan Pavkov in the first half. Photograph: Andrew Boyers/Action Images via Reuters

Spurs had travelled in the belief that Red Star on home turf would be a different proposition to the team that had slumped to a 5-0 defeat in north London two weeks ago. The statistics offered the warning. In 21 previous European home ties, Red Star had lost only two while exactly a year ago they had beaten Liverpool 2-0. Yet after a cagey opening, in which Milan Pavkov blew a gilt-edged one-on-one with Paulo Gazzaniga, shooting too close to the goalkeeper, Spurs asserted themselves.

Pochettino had shuffled his pack, starting Juan Foyth at right-back and Eric Dier in central defence, but Lo Celso was the headline news item. The loanee from Real Betis, whom Spurs have the option to buy for £55m next summer, had previously played only 74 minutes for Spurs. He was in action until 6 July at the Copa América with Argentina and did not sign until 8 August – transfer deadline day in England – having missed pre-season entirely.

Lo Celso’s time at Spurs has been characterised by fitness struggles and mutterings from Pochettino that he has been some way off the pace. Here, it was possible to see what he will bring to the team. Playing on the right of midfield, he showed off his change of pace and an eagerness to pass the ball with zip and directness.

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Lo Celso began the move which led to the breakthrough goal, pouncing on Dusan Jovancic to win possession and release Harry Kane, although a good deal would happen before he jabbed his shot past Milan Borjan.

Kane’s first touch looked heavy but he got to the ball before Borjan to poke a shot against the foot of a post. When Son’s follow-up attempt was hacked off the line, it appeared that the danger had passed. Yet Ndombele recycled the move, crossing for Kane, who flashed a volley across the face of goal. Son stretched to divert the ball up and against the crossbar and, after a further scramble, Lo Celso took a touch and prodded home.

Red Star might have feared it would not be their night when they also hit the frame of the goal twice in the same move on 44 minutes, only this time there would be no finish. Rajiv van La Parra rattled the foot of the near post and, when Davinson Sánchez accidentally looped the rebound towards his own goal, it came back off the crossbar.

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Red Star’s end product was missing. Witness Pavkov’s decision to pass rather than shoot when well-placed early in the second half – he got it all wrong – and Spurs turned the screw thereafter.

There is a swashbuckling quality to Ndombele and he drove hard into the final third before whipping the ball over to Dele Alli, who played in Son with a perfectly weighted assist. Son thrashed the ball past Borjan before he added his second shortly afterwards. It was another nicely worked team effort.

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Kane got Danny Rose in behind the Red Star defence and the full-back’s low cross invited Son to tap home.