Once again this week, Novak Djokovic indicated that he's ready to hit the reset button. Once again, the button has shorted out. The target on his back is so big now that it's larger than his shirt. He has ducked behind the same screen as other champions who seem tired of warding off rivals, talking about his indifference to the top ranking, his family life, his desire to remain healthy enough to enjoy a long career.

Friday, the focus was again on his suffering game. It was the legs and lungs that let down Djokovic in his Monte Carlo Masters quarterfinal with David Goffin. He was failed by the same appendages and organs that not very long ago worked in concert to turn the Serbian into an impregnable, seemingly unbeatable champion.

Novak Djokovic has looked nothing like the player who won last year's French Open. Clive Brunskill/Getty Images

The irony was abundant everywhere you turned during and after this latest setback for Djokovic. Goffin, ranked No. 13, is famous for his slight, 5-foot-11, 150-pound frame. Yet there he was, near the end of the 2-hour, 37-minute match, tagging one more unpredictable down-the-line backhand winner, throwing what weight he has into one more flying inside-out forehand.

By the time Goffin won it, 6-2, 3-6, 7-5, Djokovic was hitting numerous shots off balance and huffing and puffing as if he had spent all his time running uphill while Goffin skimmed over level ground. In the match-concluding game, Djokovic was hit with a time violation before the penultimate point that he accepted without complaint because the previous rally had left him so gassed.

Across the net, Goffin breathed evenly through his nose, looking frayed but fit.

Despite the breather, Djokovic still made an inside-out forehand error, and then surrendered the match when he nearly fell over backward as he smacked a forehand error.

Djokovic's loss will overshadow the fact that Goffin played a terrific match. After a superb first set, Goffin had Djokovic on the ropes early on the second. But the No. 2 ranked player slipped away and mounted a furious, successful comeback.

Goffin appeared beaten when he fell behind a break in the third, but he rallied and showed exceptional mental strength and stamina. He didn't just go tripping through the storied "zone" on this occasion. He got down in the dirt with a baseline brawler and rose on his clay-stained legs the winner.

Goffin is an aficionado's player, but he's always seemed like Djokovic Lite. Their record bears it out. In five previous meetings, Goffin had managed to win just one set, and that was back in 2015. Djokovic has traditionally punished Goffin's assailable second serve, and overwhelmed him in the kind of rally game they both prefer.

But Goffin has made strides in the past two years. He has built on his reputation as an excellent tactician. He's as light as ever on his feet, and there's a delightful balance to his game. Lately, his willingness to change the direction of the ball during a rally -- a Djokovic trademark -- has improved, and so has his second serve.

All those factors mitigate this unexpected result. Still, it doesn't fully explain how Djokovic let his 4-2 third-set lead slip away.

At the end of last year, when Djokovic surprised everyone by ending his highly successful partnership with "supercoach" Boris Becker, the jilted coach told Sky News that Djokovic simply hadn't been working as hard after he completed his career Grand Slam by claiming his 12th major title at the French Open in June.

Djokovic's work ethic will again come into question, especially after he physically gave out in the late stages of the Goffin match.

Djokovic is just 14-4 so far this year with one title he won at the beginning of the year. The lengthy rest periods already built into his schedule, combined with all the extra time off mandated by all his losses means that Djokovic has a lot of free time on his hands.

Just what he's doing is anybody's guess.