Rafael Nadal will face the first real test of his French Open title credentials in a rematch of last year's final against David Ferrer.
The pair will clash in the quarter-finals this time after both men came through fourth-round matches on Monday, Nadal dropping just four games against Dusan Lajovic.
The eight-time champion has looked in fine fettle despite complaining of a recurrence of the back problem that affected him so badly in the Australian Open final against Stan Wawrinka.
But he has not faced anyone ranked higher than 57 - so fifth seed Ferrer will be a significant step up.
The 32-year-old was well beaten last year but this match, his 10th consecutive grand slam quarter-final, will have an extra edge because of the outcome of their last meeting.
In Monte Carlo in April, Ferrer beat Nadal on clay for the first time in 10 years, one of three defeats the world number one has suffered in the build-up to Roland Garros.
Nadal, who was watched by singer Prince, said: " Always when you have a loss in the last confrontation, that can affect (the match). Or not. I don't know.
"But the important thing for me is I am in the quarter-finals here. I am happy with the way that I arrived here.
"I think that I am a little bit better than when I was playing against him in Monte Carlo, but I think he's playing great, too. He played three weeks in a row at a very high level.
"He's coming to the match with confidence and with confidence that he beat me the last time, so it's an extra thing for me. It will be a tough one."
While Nadal is still firmly ensconced on his throne as the king of clay, the monarch of Spain, King Juan Carlos, on Monday announced his intention to abdicate in favour of his son.
"We were very surprised with this announcement," said Nadal. "The only thing I can do is to thank his majesty, the king, for everything he did all along these years.
"I had the great opportunity of meeting him on quite a few occasions. On a personal note, he was always very nice to me, very warm. He made me feel very comfortable each time we met."
Ferrer lost his first set of the tournament but was nevertheless impressive in a 6-3 6-3 6-7 (5/7) 6-1 victory over big-serving South African Kevin Anderson.
Last year's final was the Spaniard's first at a grand slam and he hopes he will cope with the occasion better when he meets Nadal again on Wednesday.
Ferrer said: "I was very nervous. I was jittery. It was a little bit too much for me. I think that I will be calmer, more serene. I don't know exactly what will be my state of mind when I play against Rafa, but I won't think about the final that took place last year.
"I will try to play aggressively with my forehand and try to finish the points at the net. But of course it's going to be difficult."
Much of the focus in the build-up to the tournament centred on Nadal's perceived vulnerability after an unusual number of clay-court losses, but Ferrer does not subscribe to the theory.
He said: "He's number one in the world, in the race he's number one. Rafael won one Masters 1000 in Madrid, played the final with Djokovic (in Rome). It was a close match.
"Rafael is always the favourite and it's always difficult to beat him."
French showman Gael Monfils is through to the quarter-finals for the fourth time in Paris but first since 2011 after an unusually straightforward 6-0 6-2 7-5 win over Guillermo Garcia-Lopez.
In the previous round Monfils had played the craziest match of the tournament against flamboyant Italian Fabio Fognini, recovering from losing the fourth set to love to win in five.
The 23rd seed said: "Maybe I was a bit withheld. I was afraid of how my body would react, because the previous match took a toll on me.
"So I tried to be extremely accurate. I thought it went well. Every day I gather more steam and power, and every time I win, then I improve and I play better."