Stan Wawrinka narrowly avoided becoming the first men's defending champion ever to lose in the first round of the French Open.
The third seed, who played the match of his life to beat Novak Djokovic in the final 12 months ago, trailed Lukas Rosol by two sets to one but hit back to win 4-6 6-1 3-6 6-3 6-4 in three hours and 11 minutes.
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Rosol was the man who famously stunned Rafael Nadal in the second round at Wimbledon in 2012 and he was on similar form here in the early stages.
Heavy rain delayed the start of play for nearly two and a half hours and Wawrinka did not enjoy the heavy conditions.
He was starring down the barrel at 2-2 and two break points down in the fourth set but saved both and from there he had the upper hand.
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A trademark backhand pass down the line helped him get the crucial break for 5-3 and Rosol was unable to threaten him unduly in the decider.
Eighth seed Milos Raonic is also through to the second round after defeating former top-10 player Janko Tipsarevic 6-3 6-2 7-6 (7/5).
Tipsarevic has had a terrible time with injury and illness and, now ranked 680, was making his first appearance at Roland Garros since 2013.
The weather has dominated the first two days of the tournament and things are unlikely to get better any time soon with plans for a roof over Philippe Chatrier now not expected to be realised until 2020.
Roland Garros has fallen well behind the other grand slam tournaments in terms of facilities for players and spectators but the French Tennis Federation has been frustrated in its efforts to improve the venue.
Having decided to stay at the historic site next to the Bois de Boulogne, the federation has run into trouble over plans to expand into the neighbouring botanic gardens.
Residents and environmentalists have so far successfully blocked the plans, with a verdict not due on the latest appeal until September.
Tournament director Guy Forget said: " When you go through two days like this you realise the importance of having a roof over your courts.
"I think it's a question of respect to the crowd and to the players that are waiting hours and hours in the lounges and in the locker rooms.
"While Wimbledon, Melbourne, and New York now have the new roof, we'll have to wait until 2020 to have ours."
Expressing frustration with the bureaucracy involved, Forget said with a smile: "Welcome to France. The red tape in France - it's a process.
"We play by the rules. We asked for planning permission a long time ago. All we can do is monitor the situation and follow the due process."