Melbourne - Alexander Zverev said his game was on the up after a poor start to the year as he came through three tight sets to beat 98th-ranked Egor Gerasimov at the Australian Open on Thursday.
The German seventh seed has been practising up to seven hours a day after a dismal ATP Cup and the hard work paid off as he safely reached the third round.
"Definitely much better than the ATP Cup. Now in the third round, I'm very happy about that," said the 22-year-old, who beat Italy's Marco Cecchinato in the first round.
The 6ft 6ins (1.98m) Zverev sent down so many double faults at the ATP Cup that Belinda Bencic suggested he donate to Australia's bushfires appeal for each one.
But his serve, a key focus of his extended practices, was a weapon once again on Thursday as he fired nine aces against no double faults, with a first-serve percentage of 78 percent.
"Sometimes it's difficult, sometimes it's easy," Zverev said when asked what it was like trying to rediscover form.
"The last week or so when we were practising, we were spending six or seven hours a day on court trying all kinds of things to find my game."
Zverev will next play Fernando Verdasco or Nikoloz Basilashvili as he attempts to match his best Australian Open result after reaching the round of 16 last year.
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