"I just completely lost rhythm, everything, struggled a little bit with the health the last couple of weeks".
The former world No. 1 is making a cautious return to the ATP Tour after stopping his 2017 season following Wimbledon, due to a right elbow injury.
"I played the best set of the whole match, and that was really good".
Federer blasted six aces, had one double fault and won 89 percent of his first serve points, losing just three points on his serve the entire match.
Daniel, who is ranked 109th in the world, advanced to the third round, where he will face Gael Monfils of France, who outlasted American John Isner 6-7 (5-7), 7-6 (7-3), 7-5.
The match was tied 2-2 in the second set when it was halted Saturday.
"Maybe it was because it was the first time he ever played against me".
Federer returned to stadium court on Sunday afternoon and needed an hour to finish off his second round victory 6-3, 7-6 (8-6).
"I was feeling like he was not loving my slice and I was also mixing in dropshots", said Federer who extended his flawless record this season to 14-0.
GETTYFederico Delbonis beat Roger Federer in their only previous meeting
Federer is making his 17th appearance in the California desert and is assured of remaining world No1 if he makes it to the semifinals.
Federer improved to 65-5 since returning from a left knee injury past year with his third-round victory in a rare day match Monday. Djokovic even admitted that he lacked rhythm in the game.
"I actually was explosive out there today and I felt good", he said.
"But it's not easy to deal with this kind of frustrations after injuries or when you always be the favorite to win a tournament, you come here and you lose in first round".
"It is still early stages for Novak coming back and the first one after surgery".
"I think it's only (a matter of) time to get where he deserves to be", said Del Potro.
"But he's strong enough to deal with that, and I love him and I want to see him in the top positions very soon".
Kasatkina has beaten all four of the current Grand Slam champions in the past year: French Open victor Jelena Ostapenko, Australian Open victor Caroline Wozniacki, Wimbledon victor Garbine Muguruza and now Stephens.