For years the concept of Chelsea as a model of sustainable transfer dealing seemed more preposterous than beach parties on Pluto. Yet here we are on the verge of a new Premier League season for which the Londoners have spent less on new players than they have raised from flogging unwanted ones. How did this happen? Has anyone told Roman Abramovich?

When the Russian sanctioned the purchase of Glen Johnson from West Ham just after buying Chelsea in the summer of 2003, it was the start of a season-long splurge that resulted in a net transfer loss of about £150m. The following season, buys exceeded sales by £139m. Balancing the books did not seem like something that Abramovich could be bothered with.

Sure enough, for most of the past decade Chelsea have been among the first accused whenever opponents such as Arsène Wenger rail against “financial doping”. Yet Chelsea always claimed, usually to much scoffing, that they would one day become self-sufficient and this summer’s transactions suggest that, at least when it comes to transfer fees, the club may be devising a method of operating that does not depend on permanent indulgence by their owner. The fees for Diego Costa, Cesc Fábregas, Filipe Luís and Mario Pasalic were more than offset by those received for David Luiz, Romelu Lukaku, Demba Ba and Patrick van Aanholt, generating a profit of about £2m. So far this summer, Arsenal, Liverpool and the Manchester clubs are all deep in the red as far as transfers are concerned.

Caution is required here and not only because there are plenty of other aspects of a club’s accounts. This is not the first time that Chelsea have been in the black in terms of transfer fees: they also made a profit in the 2008-09 season when the newly flush Manchester City lurched in to take Wayne Bridge, Shaun Wright-Phillips and Tal Ben Haim off their hands. That seemed more like serendipity than good strategy and the following season Chelsea made a net loss on transfers of £22m. In January 2011, Abramovich ordered the purchase of Fernando Torres for £50m, which, on top of captures including David Luiz and Ramires, contributed to a seasonal loss of nearly £90m. Goodnight, prudence.

Now, however, even though they are unlikely to find anyone to hand over £50m for another David Luiz every year, Chelsea appear to be reaping the fruit of a well-laid plan. It is a different plan to the one that they originally tried. Back in 2005 the club lured a reputed top talent spotter, Frank Arnesen, from Tottenham Hotspur and appointed him director of football as part of a bid to cultivate their own talent and feed a constant supply of youngsters into the first team while supplementing the side with the occasional big signings.

Arnesen was a major influence in the acquisitions of Mikel John Obi, Salomon Kalou and Florent Malouda but few of the younger players that arrived during his five years at Stamford Bridge made an impact on the first team. The latest strategy does not require youngsters to make it into Chelsea’s first team at all. It does not even depend on Chelsea developing them because they can get others to do that for them.

Last season Chelsea had 18 players out on loan at other clubs and the season before they had even more. Only Thibaut Courtois and possibly Kurt Zouma (bought from St-Etienne in January before being loaned straight back) have done well enough to convince José Mourinho they are ready to feature in his team. Plenty of others did well enough to persuade other clubs to buy them.

Everton forked out a record £28m for Lukaku. Back in January, Wolfsburg paid about £18m for Kevin De Bruyne. The two Belgians made three Premier League starts for Chelsea, who nonetheless made a combined profit of more than £21m on them in three years. They could make even bigger gains from Courtois and Eden Hazard if they wished, or even from Eden’s brother Thorgan, who has just gone to Borussia Mönchengladbach for his second loan spell away from Chelsea since joining in 2012.

Seven other youngsters have already gone back out on loan after stints away last term, as has Pasalic, who joined Elche soon after arriving at Stamford Bridge from Hajduk Split. One of the teenage recruits from the Arnesen era, Gaël Kakuta, has just been farmed out for the sixth time, while another, Van Aanholt, has been sold to Sunderland for about £2m.

There is always the risk of repeating the Nemanja Matic mistake. After buying the Serbian for £1.5m in 2009, Chelsea sent him on loan to Vitesse Arnhem before selling him to Benfica for £21m in 2011 – but that move did not look so clever when, last January, Matic was bought back for the same fee to banish some of the midfield vulnerability.

Chelsea, though, are presumably confident that their judgment will be right far more often than not. As for the broader question of whether all this is right is debatable, even if it helps Chelsea comply with the rules of financial fair play. If all big clubs expand their efforts to stockpile young players to lease out and sell like landlords using a property empire to extend their privileges, it gives them an even greater degree of control over the market. Smaller clubs paying more to keep the aristocracy’s accounts in rude health might be considered an affront to decency.

That is patently not Chelsea’s concern. They want to perpetuate their power and win more titles. This summer’s activity looks to have left them well placed to do that. The new acquisitions have not made holes in their pocket, just filled gaps in the team.

Luís is a dynamic left-back whose arrival could allow the excellent César Azpilicueta to shift across to his preferred role on the right. Fábregas should provide more goals and drive from midfield on a platform manned by Matic or the fit-again Marco van Ginkel. Oscar could also join a central midfield trio if Mourinho chooses to switch formation to the 4-3-3 that he has tended to prefer in the past.

Either way, Fábregas looks an ideal heir to Frank Lampard, whose departure, like that of Ashley Cole following Luís’s arrival, no doubt helped lighten the payroll. Chelsea’s midfield was fragile at times last season but now looks fearsome and Fábregas, if he resumes where he left off in the Premier League with Arsenal, should become a regular starter and produce more consistency than Hazard and Oscar, who were outstanding at times last season but who also shrivelled up at crucial moments. Being older and stronger, Hazard and the Brazilian should improve this term, as should André Schürrle, Ramires and Mohamed Salah.

The chief reason Chelsea finished behind Manchester City and Liverpool last season was that they scored 30 goals fewer than those teams and that was largely because of the shortcomings of their strikers. Costa looks like a big part of the solution to that problem.

The £32m recruit from Atlético Madrid seems the ideal Mourinho centre-forward, a warrior who has the power, mobility, cunning and sharpness to serve as a one-man front line. Last season Costa made Atlético fans forget about their departed hero, Radamel Falcao, by plundering 35 goals in 44 matches as Real Madrid’s little neighbours won La Liga and reached the Champions League final. He has the capacity to banish Chelsea fans’ bad memories of last season’s strikeforce but to do so, he will need to avoid injury and adapt to the Premier League instantly. Otherwise, Chelsea will find themselves banking on the returning 36-year-old Didier Drogba and dear old Torres.

That, perhaps, would be an interesting time to reassess the price of Chelsea’s summer frugality.