"This is how this game has been played for decades," Federer said. "We're used to walking on and off the court and being flexible about these kind of things."
Federer lost serve just once against Falla, at 5-all in the opening set, but broke back and hit four winners in the tiebreaker. From there only rain could slow Federer - the match was stopped for 15 minutes in the second set and for an hour in the third.
"The texture of the clay changes drastically when there's no sun," he said. "Conditions slow down a lot. ... There are advantages and disadvantages, and you've got to use them if you can."
Federer, who completed a career Grand Slam when he won at Roland Garros last year, is seeking his 17th major title.
No. 5-seeded Robin Soderling won 20 of the first 22 points and went on to beat unseeded American Taylor Dent 6-0, 6-1, 6-1. Soderling, who upset Rafael Nadal last year and then lost to Federer in the final, has lost seven games through two matches.
Other men's winners included No. 8 Jo-Wilfried Tsonga, No. 10 Marin Cilic and No. 11 Mikhail Youzhny before rain interrupted the day's play for a second time.
Venus Williams used her big serve to beat Arantxa Parra Santonja of Spain 6-2, 6-4, improving to a 14-2 win-loss record on clay in 2010. She's seeded second at Roland Garros behind younger sister Serena, who scouted from behind the baseline, sitting next to their father. The sisters could meet in the final.
In other women's play, No. 26 Dominika Cibulkova of Slovakia rallied past Varvara Lepchenko of the United States 4-6, 6-2, 6-0. Cibulkova, a semifinalist last year, faces Williams next.
"I'll continue to try to execute my game and not worry really a ton about what my opponent is doing," Williams said. Serves at up to 128 mph (206 kph) kept her in control of her match, and she was never broken.
Two-time semifinalist Nadia Petrova, seeded 19th, beat Agnes Szavay of Hungary 6-1, 6-2. No. 14 Flavia Pennetta defeated Roberta Vinci 6-1, 6-1 in an all-Italian match.
For the day's opening match on center court, Williams again wore her lacy corset despite a brisk change in the weather, with mostly cloudy skies and temperatures in the 60s F (high teens C). At her postmatch news conference, there were seven questions about her outfit.
"Lace has never been done before in tennis, and I've been wanting to do it for a long time," she said. "The illusion of just having bare skin is definitely for me a lot more beautiful."
Williams sent her flounce flying when she served. She went to deuce six times in her first service game before holding, then pulled away to take the set.
In the second set, both players held until the seventh game. Williams drew Parra Santonja into a moonball rally, then sprinted forward to slam a winner. That gave Williams a 4-3 lead, and she served out the victory, her 28th in 32 matches this year.
In 13 previous French Open appearances, Williams reached the semifinals only once - in 2002, when she lost to Serena in the final. But at 29 she's enjoying a career resurgence, and her record this year is the best on the women's tour.
Soderling remained on course for a Roland Garros rematch against Federer in the quarterfinals.
"I'm feeling good," Soderling said. "I won two matches pretty easy in straight sets, and I didn't have to run for many hours on court so far, so I feel fresh."
Tsonga, France's best title hope, defeated countryman Josselin Ouanna 6-0, 6-1, 6-4. Cilic swept Daniel Gimeno-Traver of Spain 6-3, 7-6 (4), 6-2, and Youzhny rallied past Lukas Lacko of Slovakia 6-7 (8), 6-3, 6-3, 6-2.
