Melbourne - World No 5 Dominic Thiem admitted he was "freaking out" after dropping two sets before regaining composure to beat gutsy home hope Alex Bolt at the Australian Open on Thursday.
The Austrian, targeting a maiden Grand Slam crown, looked fragile as the crowd got behind the wildcard but ultimately prevailed 6-2, 5-7, 6-7 (5/7), 6-1, 6-2 in 3hrs 22mins.
Thiem is among a clutch of players tipped to win a Major after reaching the last two Roland Garros finals, but he was exposed at times by a player ranked 140 who controlled much of the second and third sets.
"I got crazy today in the third set. I think body language was not the best because it was, of course, in my head that I should be 2-0 up, 6-2, 6-4, I should be up. I messed it up," he said.
"Instead of that, he raised really his level. The crowd got it going.
"It was all of a sudden a really tight third set that shouldn't happen. That's why I was freaking out inside and also outside today."
Thiem, who has never gone past the fourth round in six previous attempts, ultimately came through to set up another tricky clash in the third round, against either American 29th seed Taylor Fritz or big-serving South African Kevin Anderson.
He looked comfortable after racing through the opening set and was serving at 5-4 to go two sets in front. But the crowd was roaring for Bolt and he remarkably broke, with the tide turning as he rallied to clinch the set 7-5.
The third set was a tight affair with neither player giving an inch. Thiem had an opportunity at 4-4 with two break points but he failed to convert.
The Austrian's best efforts were being met with resistance, with Bolt saving another three break points on his next service game, leaving Thiem frustrated at his missed opportunities.
It went to a tiebreaker and Bolt raced into a 6-2 lead, but wobbled as Thiem won three points in a row before the Australian sent down a booming ace to got two sets to one in front.
However, Thiem recovered his composure and after a series of long baseline rallies broke twice to take the match into a deciding set.
The Austrian's focus and fitness proved decisive in the fifth, with a Bolt forehand into the net giving him a break and he raced to victory as his opponent flagged.
Thiem insisted that playing five sets in the second round would not hurt his chances in Melbourne.
"It was nice conditions, was not hot," he said. "There's a big difference if you play three hours 20 (minutes) in these conditions or if you play four-and-a-half when it's 40 degrees outside."
Results on day four of the Australian Open Grand Slam at Melbourne Park on Thursday (x denotes seeding):
Rafael Nadal (ESP x1) bt Federico Del Bonis (ARG) 6-3, 7-6 (7/4), 6-1
Pablo Carreno-Busta (ESP x27) bt Peter Gojowczyk (GER) 6-4, 6-1, 1-6, 6-4
Nick Kyrgios (AUS x23) bt Gilles Simon (FRA) 6-2, 6-4, 4-6, 7-5
Karen Khachanov (RUS x16) bt Mikael Ymer (SWE) 6-2, 2-6, 6-4, 3-6, 7-6 (10/8)
Gael Monfils (FRA x10) bt Ivo Karlovic (CRO) 4-6, 7-6 (10/8), 6-4, 7-5
Ernests Gulbis (LAT) bt Aljaz Bedene (SLO) 7-5, 6-3, 6-2
Taylor Fritz (USA x29) bt Kevin Anderson (RSA) 4-6, 6-7 (5/7), 7-6 (7/4), 6-2, 6-2
Dominic Thiem (AUT x5) bt Alex Bolt (AUS) 6-2, 5-7, 6-7 (5/7), 6-1, 6-2
Daniil Medvedev (RUS x4) bt Pedro Martinez (ESP) 7-5, 6-1, 6-3
Alexei Popyrin (AUS) bt Jaume Munar (ESP) 6-2, 7-6 (7/5), 6-2
John Isner (USA x19) bt Alejandro Tabilo (CHI) 6-4, 6-3, 6-3
Stan Wawrinka (SUI x15) bt Andreas Seppi (ITA) 4-6, 7-5, 6-3, 3-6, 6-4
David Goffin (BEL x11) bt Pierre-Hugues Herbert (FRA) 6-1, 6-4, 4-6, 1-6, 6-3
Andrey Rublev (RUS x17) bt Yuichi Sugita (JPN) 6-2, 6-3, 7-6 (7/5)
Fernando Verdasco (ESP) bt Nikoloz Basilashvili (GEO x26) 4-6, 7-6 (7/5), 6-4, 6-4
Alexander Zverev (GER x7) bt Egor Gerasimov (BLR) 7-6 (7/5), 6-4, 7-5
Belinda Bencic (SUI x6) bt Jelena Ostapenko (LAT) 7-5, 7-5
Anett Kontaveit (EST x28) bt Sara Sorribes (ESP) 6-2, 4-6, 6-1
Donna Vekic (CRO x19) bt Alize Cornet (FRA) 6-4, 6-2
Iga Swiatek (POL) bt Carla Suarez (ESP) 6-3, 7-5
Elise Mertens (BEL x16) bt Heather Watson (GBR) 6-3, 6-0
Catherine Bellis (USA) bt Karolina Muchova (CZE x20) 6-4, 6-4
Yulia Putintseva (KAZ) bt Danielle Collins (USA x26) 6-4, 2-6, 7-5
Simona Halep (ROU x4) bt Harriet Dart (GBR) 6-2, 6-4
Garbine Muguruza (ESP) bt Ajla Tomljanovic (AUS) 6-3, 3-6, 6-3
Zarina Diyas (KAZ) bt Anna Blinkova (RUS) 4-6, 6-3, 6-4
Kiki Bertens (NED x9) bt Arina Rodionova (AUS) 6-3, 7-5
Camila Giorgi (ITA) bt Svetlana Kuznetsova (RUS) 6-3, 6-1
Angelique Kerber (GER x17) bt Priscilla Hon (AUS) 6-3, 6-2
Anastasia Pavlyuchenkova (RUS x30) bt Taylor Townsend (USA) 7-5, 7-6 (7/1)
Karolina Pliskova (CZE x2) bt Laura Siegemund (GER) 6-3, 6-3