Novak Djokovic survived a serious test of his French Open credentials by defeating Diego Schwartzman in five sets.
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.
The 24-year-old is only 5ft 7in but 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.
Coach Andre Agassi did not make an appearance on Court Philippe Chatrier until midway through the second set, and Djokovic revealed after the match their partnership is set to continue in the long term.
Agassi said in an interview on Friday he is planning to come to Wimbledon, and Djokovic hopes the American will be with him for all the biggest tournaments.
"He was not supposed to be here today, because we have finished yesterday with our in-person collaboration here in Paris," said the Serbian.
"He managed to reschedule certain things and show up today. I appreciate that.
"I hope we can create something that is going to go long term. We don't have anything set in stone. He's going to try his best to be in the biggest tournaments with me.
"Of course we both agree that I'm going to need someone also on a day-to-day basis that can work with him, but he's the man."
On his performance, Djokovic said: "He was the better player probably for the first three sets. And then the fourth and fifth sets went the way I hoped that the whole match can go.
"I'm glad that I have some positives to take from today's match. I was mentally still strong and as calm as I could be. It was just too many unforced errors from myself."
Rafael Nadal laid down a marker as he chases his 10th French Open title with his most one-sided ever victory at Roland Garros.
The fourth seed and favourite to lift the Coupe des Mousquetaires next Sunday allowed Georgia's Nikoloz Basilashvili just a single game in a 6-0 6-1 6-0 victory.
It is the first time in a completed match at the tournament that Nadal has only lost one game.
The biggest cheer of the match came when Basilashvili finally won a game at 6-0 5-0.
But that proved to be as good as it got for the Georgian, whose final tally of five winners and 34 unforced errors rather told its own story.
Nadal hit 27 winners, most of them off his lasso forehand, which is in ominously good shape.
Basilashvili looked like he might be saved by the weather as thunder rumbled overhead late in the third set.
Nadal afforded himself a chuckle as Basilashvili wasted a bit of time by changing his racket.
But the rain did not arrive and he was put out of his misery after an hour and a half, with Nadal moving through to a fourth-round clash with fellow Spaniard Roberto Bautista Agut.
Roland-Garros heartbreak for injured David Goffin.
— Roland-Garros (@rolandgarros) June 2, 2017
Read: https://t.co/ceD624T1qF #RG17 pic.twitter.com/YKX7PnmpM1
Tenth seed David Goffin was forced to retire during his third-round after suffering an ankle injury in a fall.
The Belgian was leading Horacio Zeballos 5-4 in the opening set on Court Suzanne Lenglen when he tripped over the covers at the back of the court.
Goffin, who was chasing a high shot from his opponent, immediately clutched at his right ankle and received lengthy treatment.
He was helped off court and news soon came through of his retirement, with Zeballos sportingly carrying the Belgian's bag back to the locker room.
The injury is hugely unfortunate for Goffin, who has had an excellent season and arrived at Roland Garros as a dark horse.
He will now hope to be fit for Wimbledon in four weeks' time.
There was another retirement on Court 2, where Spain's Guillermo Garcia-Lopez pulled out when trailing fifth seed Milos Raonic 6-1 1-0.
Sixth seed Dominic Thiem is yet to drop a set and ended the brave run of Steve Johnson with a 6-1 7-6 (7/4) 6-3 victory.
The pair shared an emotional hug at the net, with Johnson having lost his father less than a month ago.
Pablo Carreno Busta reached the fourth round at a grand slam for the first time, recovering from losing the first four games to beat Grigor Dimitrov 7-5 6-3 6-4.
