World No 6 Stefanos Tsitsipas was pushed to a marathon five sets by wildcard Thanasi Kokkinakis before making the Australian Open third round.
The Greek dropped only four games in his first-round match, but faced a far sterner challenge from the 267th-ranked Australian.
He finally came through 6-7, 6-1, 6-1, 6-7, 6-4 but needed 4hr 32min to do it on muggy day at Rod Laver Arena.
"I just want to have an ice bath right now," said a relieved Tsitsipas.
"He is a great competitor, a great fighter and it was very difficult facing him today. He has a great serve and all the weapons from the baseline.
"Was a hell of a day."
The 22-year-old next plays Swede Mikael Ymer, who beat promising Spanish teenager Carlos Alcaraz.
Tsitsipas went into the match as hot favourite, having demolished Gilles Simon in his opening match and never having lost a Grand Slam match to a player ranked as low as Kokkinakis.
He has a solid record against Australians, with Nick Kyrgios, who was watching in the stadium, the only one to ever beat him.
But Kokkinakis, who has been plagued by injury and illness during his career, fought hard.
With the home crowd becoming ever more vociferous in their support, he gave as good as he got in a close first set, with both players trading blows in long rallies and big serves.
The Australian saved two set points at 4-5 and took it to a tiebreaker, where he prevailed on the back of a Tsitsipas double fault.
But the Greek's superior firepower and fitness came to the fore in the second set and by the third Kokkinakis appeared to be running out of steam, unable to match Tsitsipas' consistency.
He found a second wind, though, in the fourth set and after saving a match point at 4-5 took it to a fifth, buoyed by the energy of the crowd.
However, Tsitsipas' unrelenting return on serve wore him down and he got a decisive break in fifth game as Kokkinakis tired.
Tsitsipas, into the third round for third successive year, is looking to better his 2019 effort when he made the semi-finals, beating Roger Federer before losing to Rafael Nadal.
Evergreen Lopez outlasts Sonego
Feliciano Lopez is only second to Roger Federer when it comes to longevity on the Grand Slam circuit and the Spanish veteran, at the age of 39, proved on Thursday he still has plenty of gas in the tank to win a brutal five-set contest.
Lopez rallied from two sets down to beat Italy's Lorenzo Sonego 5-7, 3-6, 6-3, 7-5, 6-4 and book a place in the Australian Open third round for the first time since 2016.
When asked how highly he rates his latest five-set rescue job, an "exhausted" Lopez said: "Well maybe pole position.
"As you know, to win a match in a Slam for me now is very special. If I do it the way I did today, even more."
World No 65 Lopez is playing a record-extending 75th consecutive Grand Slam event, having not missed any since the French Open in 2002.
Only Federer, who has skipped this year's Australian Open due to an injury, has played more Slams overall, with 79 compared to Lopez's tally of 76.
Lopez fondly remembers his major debut at the French Open in 2001, even if it ended in a straight-sets defeat.
"I think I got killed in the first round by Carlos Moya, if I'm not wrong," Lopez said. "I qualified and I lost to him. He was my idol when I was growing up."
Lopez recently became a father and said he was unable to spend enough time on the court before arriving in Australia.
"I'm exhausted, obviously. I was already tired the first day when I won my first match, so even more today," he added.
"For me to win today I think it's above any expectations."
Lopez will next face in-form Russian Andrey Rublev, seeded at seven, for a place in the last 16.