PARIS - Novak Djokovic seemed well on his way to yet another ho-hum victory, yet another French Open final, yet another matchup against rival Rafael Nadal. And then, suddenly, what had been a gallop became a grind.

Slightly more than two hours into his semifinal against Stefanos Tsitsipas on Friday night, Djokovic was serving for the match, one point from ending things in straight sets. But a down-the-line backhand veered a tad wide, Djokovic rolled his eyes and, eventually, he was somehow pushed to five sets.

As is usually the case, Djokovic got back in gear down the stretch to hold off the much younger, much less accomplished Tsitsipas 6-3, 6-2, 5-7, 4-6, 6-1 to reach his fifth title match at Roland Garros.

“I stayed calm on the surface,” Djokovic said, “but deep down, it was a totally different matter.”

Standing in the way of No. 1 Djokovic, a 33-year-old from Serbia, on Sunday at Court Philippe Chatier — he is pursuing a second trophy here and 18th from Grand Slam tournaments — will be, as it’s been so often, No. 2 Nadal, a 34-year-old from Spain.

It will be their 56th meeting, the most between two men in the professional era (Djokovic leads 29-26), 16th at a major (Nadal leads 9-6) and eighth at the French Open (Nadal leads 6-1).

“It’s his house,” Djokovic said.

In addition to closing in on an unfathomable 13th French Open championship with a 6-3, 6-3, 7-6 (0) win over 12th-seeded Diego Schwartzman, Nadal now gets a chance to tie Roger Federer for the men’s record of 20 Slam titles.

Nadal said it’s fine for others to discuss such matters, but his focus remains squarely on the task at hand.

“I’m playing the most important tournament of the year — that’s what motivates me,” he insisted.

While Nadal dealt with the slightest tension late in his third set Friday, everything became more interesting at that juncture for Djokovic against Tsitsipas, a 22-year-old from Greece in his second major semifinal.

Djokovic served for the win at 5-4, holding that match point at 40-30. He would require another 1 hour, 45 minutes to finish the job.

That one misstep left the door a bit ajar, and Tsitsipas barged through. He got his first break all match when Djokovic sent a forehand long, making it 5-all. Tsitsipas broke again to steal that set.

What changed? Tsitsipas began pushing forward, taking the action to Djokovic, whose misses began to increase.

Also notable: the massive swing in success on break points.

Djokovic started by converting four of five, then went through a stretch where he was one of 13.

Tsitsipas, in contrast, began zero for 10, then went four for five.