Sane struck for the 2-1 win.
Guardiola said afterwards: "In the first half we had many chances, and after 2-0 the game was in control. We let them have the opportunity to come back.
"Once you concede with five to 10 minutes left you suffer, we didn't get the third goal which we needed. We had the chances to kill the game but we missed and that is what it is. We know that, we are not new in the Premier League.
"We had a good performance, we were aggressive and regained the balls, Ben Foster made some incredible saves.
"Leroy Sane is scoring goals, he is back. It is always difficult at Stamford Bridge, we must recover our legs and our mind."