Novak Djokovic survived the first serious test of his French Open credentials by fighting back from two sets to one down to beat Diego Schwartzman.
The defending champion had reached round three without dropping a set despite not playing his best.
But he was given a real fright by Argentinian Schwartzman before coming through 5-7 7-5 3-6 6-1 6-1.
Schwartzman, ranked 41, has never beaten a top-10 player but he has tested the likes of Rafael Nadal and Kei Nishikori this season.
The 24-year-old is only 5ft 7in tall but his shots pack a real punch and he shocked Djokovic by coming from a break down to take the opening set.
Djokovic, with coach Andre Agassi sat impassively in the stands, looked to have turned things around when he claimed the second set but Schwartzman was not finished.
At times, the second seed resembled the player whose dominance of the game was total only 12 months ago.
But there were too many unforced errors - 55 in total - and at costly times.
After Schwartzman broke for 6-5, Djokovic had four chances to force a tie-break but could not take any of them, the crowd feeding off the Argentinian's energy.
But maintaining such intensity over five sets is extremely difficult and one of the reasons the format favours the top players.
Djokovic raced into a 4-0 lead at the start of the fourth set, with his only blip coming when he dropped serve in a fiery fifth game.
Umpire Carlos Ramos penalised Djokovic a first serve for a time violation and then gave him another warning for bad language.
Djokovic argued his case while the crowd whistled and jeered, but it did not disrupt his momentum.
Schwartzman had given all he had and the champion lives to fight another day.