Germany's Alexander Zverev (left) hugs France's Jeremy Chardy after their men's singles match on day four of the Australian Open
The 21-year-old, seeded fourth at Melbourne Park, looked set for an easy outing after taking a two-set lead and with a flurry of break points in the third set. But he wasted four chances to break and then lost his serve to surrender the third set.
The Frenchman, ranked 36, won the fourth set in a tiebreak after Zverev, who claimed the 2018 ATP Tour Finals after beating Roger Federer in the semis and then Novak Djokovic, wasted four more break point opportunities in the seventh game.
Chardy ran out of steam in the final set as his errors mounted and Zverev cantered to victory in three hours and 46 minutes. He next plays local wildcard Alex Bolt, who stunned 29th-seeded Frenchman Gilles Simon 2-6 6-4 4-6 7-6(8) 6-4.