A bad start to the game at West Ham condemned Conte's side to defeat as Marko Arnautovic's sixth-minute goal proved enough to give the hosts the three points.
Chelsea tried to respond but were unable to break down a resilient West Ham team despite registering 19 shots.
"I think today we lost the game against West Ham and it was very difficult because our start was bad, we conceded the goal and it was difficult to come back," Conte admitted after the full-time whistle.
"I saw their game against Manchester City, when City attacked for the whole game against 11 defenders but they found a way to score, we created chances but didn't take them and so we are talking about a defeat. Many players were tired which is normal when you play every three days.
"Today our ideas were not so clear and in the final pass we made a lot of mistakes. Despite that we created chances to score but we didn't take them. When you shoot 19 times in a game it means you attacked, but we can do better."
Conte replaced Tiemoue Bakayoko with Pedro at half-time in an attempt to recover the situation after the French midfielder endured another disappointing performance.
However, the Chelsea boss said that he was happy with Bakayoko's display, pointing out that his withdrawal was merely a tactical decision.
"It was a tactical decision. Bakayoko was playing a good game but when you find 11 players behind the ball and you are losing 1-0, it's important to change something," Conte added.
"Pedro has different characteristics to Bakayoko, he's better one-versus-one and he has good technical qualities. Bakayoko satisfied me with his performance."
Meanwhile, Conte admitted that Chelsea's fourth defeat of the season means that the Premier League title race is now over for them.
As it stands, the Blues trail City by 11 points and could finish the weekend 14 behind the leaders if Pep Guardiola's men secure a victory at Manchester United on Sunday.
"To speak about the title race after a defeat is a bit strange, especially if this is the fourth defeat of the season, after 16 games. When you have that it's impossible to think you are in the race, my experience tells me if you want to stay in the race in the first part of the season you can lose once or twice," Conte admitted.
"After 16 games, if you lose four it means you never got started. We started with a defeat at home to Burnley. We lost another game, against Man City, but we have reasons to justify that. Then when you lose to Crystal Palace, who were bottom, and West Ham, who are in a bad position, you can lose points in these games but it means you are not in the title race."