Novak Djokovic has overcame some early jitters in his first match since his triumph at Wimbledon last month to see off Sam Querrey at the Cincinnati Masters.
Hours later on Tuesday, Federer took to centre court with only a rain interruption in the second set delaying his 6-3 6-4 win over Juan Ignacio Londero.
World No.1 and defending champion Djokovic fired his 15th ace on match point to seal a 7-5 6-1 win over Querrey and make up for his slow start on the sun-soaked courts.
"I made three double faults in my opening game and lost the break. I was quite a nervous at the start," he said of falling behind 2-0 against the big-serving American.
"I'm really glad to overcome a challenge like this and get myself going."
Djokovic, who defeated Federer in an epic final at Wimbledon, said he needed time to recover from the surge of emotions with both players not having played since their All England Club classic.
"That was one of the most epic matches I've been a part of and probably the most demanding one from the mental perspective," he said of his five-set victory.
"So it really did take me some time to recharge my batteries, especially in my head. My body was fine."
Federer takes just 61 minutes
Swiss ace Federer is chasing a record-extending eighth win in Cincinnati and was clinical in his 61-minute outing, as preparations for the US Open ramp up.
"(I'm) very happy. I thought it was tricky with the rain delay and everything, but I'm happy to be back on the courts," Federer said.
"It's totally different to the grass courts and the clay courts we have seen, so this is the beginning of a long, long hard-court swing.
"So it's nice to start off with a win."
Djokovic is aiming for a 34th Masters title at the US Open warm-up event to move to within one of Rafael Nadal's record haul of 35, which the Spaniard extended with victory in Canada.
In first-round results, Swiss Stan Wawrinka overcame Bulgaria's Grigor Dimitrov 5-7 6-4 7-6 (7-4) in a roller-coaster match.
Young American Frances Tiafoe beat Frenchman Gael Monfils 7-6 (9-7) 6-3 and Canadian Denis Shapovalov came from behind to see off Portugal's Joao Sousa 2-6 6-3 6-2.
Others to progress to the second round included seeded trio Daniil Medvedev, Roberto Bautista Agut and David Goffin while Frances Tiafoe, Reilly Opelka, Denis Shapovalov, Andrey Rublev, Diego Schwartzman and Benoit Paire also reached the round of 32.