PARIS — Sometimes, when everything’s on the line, it’s easier to play like there’s nothing to lose.

Novak Djokovic knows that drill.

Four times on a gray, drippy Tuesday at Roland Garros, Djokovic got ready to serve on the red clay and listened to the French fans cheer against him, knowing they were one point away from watching their beloved countryman, Jo-Wilfried Tsonga, take down the top player in tennis.

On all four of those match points, Djokovic summoned something — not simply a great shot but the fortitude to hit it — to keep himself in the match.

A tightrope walker if ever there were one, the top-seeded Djokovic stole away with a 6-1, 5-7, 5-7, 7-6 (6), 6-1 victory. His hopes for the “Novak Slam” intact.

He also got his refresher course on how precarious these things can be.

“I mean, if he would win, he would deserve the win, no doubt,” Djokovic said. “But that’s sport. The one that mentally pushes more in some moments and obviously gets a bit lucky, gets the win. That’s how it goes.”

Djokovic will play No. 3 Roger Federer in the semifinals, a rematch from last year, which also marks the last time Djokovic lost a Grand Slam match.

On Tuesday, Federer overcame a two-set deficit for the seventh time in his career, rallying for a 3-6, 6-7 (4), 6-2, 6-0, 6-3 win over No. 9 Juan Martin del Potro.

“You just try to push further and it’s not easy,” Federer said of the art of his comeback.

Eight months ago, Federer was on the cusp of knocking Djokovic out of another tournament — the U.S. Open — serving with two match points and the crowd cheering him on.

Back then, Djokovic clenched his jaw and gave the smallest of smiles. Then, he unleashed on a wide serve of Federer’s for a clean winner. Saved the next point, as well, and a few days later, ended up a U.S. Open champion.