All the talk in the run-up to the year's second grand slam had been about how Novak Djokovic could take Rafa Nadal's title but third seed Federer showed he still has a part to play on the Parisian clay with a 6-3, 6-4, 7-6 victory.
The thronging crowd was treated to the usual array of classy shots from the Swiss but he received an awful low bounce at a key point in the final set to show the idiosyncrasies of the surface.
"I guess the disappointing part here in this whole story, because I'm hearing a lot of conversations about the balls, it's just that they're not the same from what we've just played for the last month," an increasingly moody Federer told a news conference.
"That for us is the most frustrating part...the tournaments all changed to the Roland Garros ball after last year. Roland Garros has changed their balls again. Now we're stuck with a different deal for all the different ATP Tour events." World number four Andy Murray has echoed Federer's view that it is better to use the same balls throughout the clay season.
Federer, the 2009 winner in Paris, achieved a break in each of the first two sets to race ahead before triumphing in the tiebreak thanks to Lopez netting on his own serve and double-faulting.
The Spaniard almost beat Federer for the first time in Madrid this month but never really threatened on center court.
Federer, who sealed victory with an effortless ace, next meets little known Frenchman Maxime Teixeira but was already looking further ahead as the record grand slam title holder bids to end the constant chit-chat about Djokovic and Nadal.
"So you go through a career where you have multiple rivals and probably one main one," he said.
"For Rafa and myself it's been either one. I think that will always stay that way no matter how many times now Rafa and Novak will play each other."
