Spending the most money on players does not guarantee Premier League success, says Chelsea manager Antonio Conte.
Chelsea are top, four points clear of Tottenham and have an 11-point lead over City and 12 points over United with six games remaining.
"It's important to understand it's not always who spends more wins," he said.
"This season isn't the only season both Manchester clubs have spent a lot of money. Look at the past."
The Blues were third in Premier League spending summer after spending £123m on players including midfielder N'Golo Kante and defender David Luiz. Manchester City topped the list on £175m, while Manchester United parted with around £150m. Tottenham were fourth after spending around £70m.
Conte described the market as "crazy" after the Premier League transfer spending record was broken with six days of the summer transfer window remaining.
He says his approach is about evolution, rather than revolution, adding: "(We want) to build, also, slowly slowly to become a real power."
Chelsea are also chasing a league and FA Cup double in his first season in charge - the Blues will play Arsenal in the showpiece final at Wembley on 27 May.
Asked if clinching the Premier League would be his best achievement, Conte, who led Italian side Juventus to three successive Serie A titles, said: "Yes, for sure. For me, for the players, for the club.
"To win in England these days is not easy. Now, it's a good season. To become a great or fantastic season there is only one way: to try to win."
'I don't want selfish players'
Conte also rejected Cesc Fabregas' call for Eden Hazard to be more selfish, after the midfielder said his team-mate could reach the level of Lionel Messi if he was "selfish" and showed greater "killer instinct".
"In my team, I don't want selfish players. I prefer to lose a game than to have a selfish player," the Italian said.
"The first target for every great champion is to play for the team and to put your talent into the team. The best players in the world don't exist without a team. I don't think Messi is a selfish player.
"For me, it's sad to listen to this. I don't want my club to buy me a selfish player one day. Never. No."
Chelsea, who have suffered two defeats in four Premier League matches, will face Southampton at home on Tuesday night.
Defender Gary Cahill is Chelsea's only doubt after he missed the cup semi-final with gastroenteritis, but Conte said the England international has returned to training and could feature.