Tour veteran and one-time Australian Open finalist Jo-Wilfried Tsonga against a whipper-snapper on this way up the rankings. A whipper-snapper with all the big shots.

A young buck who got him last time - just four months ago at the US Open, also in the second round. And in three sets for good measure.

On Margaret Court Arena on Wednesday, 32-year-old Tsonga was staring at a second-straight grand slam defeat to emerging Canadian leftie Denis Shapovalov when he trailed 5-2 in the decider.

But the 15th seed dug deep and won a gripping encounter that went the distance against the 18-year-old young gun.

As the temperature started to climb at Melbourne Park, the French former world No. 5 rallied to edge Shapovalov 3-6, 6-3, 1-6, 7-6 (7-4), 7-5 in more than three-and-a-half hours.

For Shapovalov, in just his third grand slam main draw and in his Australian Open debut, it was a classic learning experience. Learning how to close out a match when it's there for the taking. And how tough it can get deep into a five-setter.

Shapovalov, considered one of the game's brightest prospects, had his nose in front, leading 5-2, and was seemingly set for a landmark win. He tightened, however, and Tsonga pounced, reeling off five straight games. Game, set and match.

"I'm tired but really happy," said the popular Frenchman, who has been troubled by a calf injury in the lead-up to this tournament tournament, said on court.

"Of course I'm tired but really happy. I did a big fight today.

"It's not easy to play against the young guns. They go for everything. It's not easy for me to defend.

"It was really difficult for me because I struggle phyically."

The youngster's eye-catching array of shots helped him take the opening set after breaking Tsonga in the fourth game.

Then a 26-minute 6-1 third set was another reminder of the Canadian's promise.

It was tight in the fourth as Tsonga used all his guile and physical presence to stay ahead on serve and take the teenager to a tiebreak. The Frenchman had it his way in the 'breaker.

But five-set contests at this level are new to teenagers, Shapovalov included, and he slipped up at the crucial juncture.

Serving for the match at 5-3, the errors came, including a double fault, allowing Tsonga to break. From there the Frenchman didn't give him another look.

Shapovalov was circumspect about his defeat and the final-set fade. "Like I said, it's a sport. I wasn't thinking about it much. Just didn't play a good game on my serve. Then he picked up his level," he said.

"Yeah, nothing too bad there. I mean, I'm just going to learn from it and keep going."

For Tsonga, it was a pleasing win against the dangerous teenager who could be likened to a more youthful version of himself.

Cast your mind back 10 years. Novak Djokovic was still a promising player and just out of his teens. Tsonga, an eye-catching 22-year-old, was crashing his way through the Australian Open field. Yes, he was eventually stopped by the Djoker on finals night but, boy, did the strapping Frenchman make an impression during that fortnight.

How the wheel turns.

Now a hardened veteran whose career-high ranking was reached six years ago, his appearance in that memorable tournament decider a decade ago - which also doubled as Djokovic's breakthrough slam - remains the Frenchman's high point at any of the majors.

Tsonga performed his characteristically animated celebration on court after a draining win.

He's alive for another day and the chance remains to break his grand slam duck.