Rafael Nadal and Daniil Medvedev booked their spots in the Australian Open third round, while Alexander Zverev and Stan Wawrinka also progressed.

Nadal remained on track in his bid to win a 20th grand slam title despite wasting chances against Federico Delbonis in Melbourne on Thursday.

The seeds have been relatively untroubled in the opening rounds in Australia, and they are on a collision course heading into the end of the first week and into the second.

Medvedev, Zverev and Wawrinka were also among the winners in the top half of the draw.

NADAL BATTLES INTO ALL-SPANISH THIRD-ROUND CLASH

Nadal converted just three of 20 break points to overcome Delbonis 6-3 7-6 (7-4) 6-1.

The Spanish star was wasteful before winning in two hours, 30 minutes, while he apologetically kissed a ball girl after striking her with a wayward forehand late in the victory.

Awaiting Nadal is Pablo Carreno Busta, the 27th seed having got past German qualifier Peter Gojowczyk 6-4 6-1 1-6 6-4.

Nadal has won his previous four meetings with Carreno Busta.

MEDVEDEV, ZVEREV AND WAWRINKA ADVANCE

Runner-up to Nadal at last year's US Open, fourth seed Medvedev was too strong for Spain's Pedro Martinez as he won 7-5 6-1 6-3.

Another member of the 'Next Gen', Zverev got the job done against Egor Gerasimov, winning 7-6 (7-5) 6-4 7-5.

Zverev will meet Fernando Verdasco after the Spanish veteran upset 26th seed Nikoloz Basilashvili in four sets.

Wawrinka, the 2014 champion, was pushed hard by Andreas Seppi, but the Swiss made it 10 wins in 14 meetings with the Italian veteran, securing a 4-6 7-5 6-3 3-6 6-4 victory.

John Isner awaits Wawrinka after the American served 32 aces in a 6-4 6-3 6-3 win against Chilean qualifier Alejandro Tabilo.

Dominic Thiem (fifth seed) and David Goffin (11th) were pushed to five sets before overcoming Alex Bolt and Pierre-Hugues Herbert respectively.

KYRGIOS, KHACHANOV SET UP CINCINNATI REMATCH

Nick Kyrgios and Karen Khachanov were both tested before setting up a third-round clash.

Kyrgios got past Gilles Simon 6-2 6-4 4-6 7-5, while Khachanov needed four hours, 34 minutes to edge Mikael Ymer 6-2 2-6 6-4 3-6 7-6 (10-8).

Khachanov won his previous meeting with Kyrgios in Cincinnati last year, but it was a clash best remembered for the Australian's outburst at umpire Fergus Murphy that resulted in a 16-week suspended ban and fine.

Gael Monfils, Andrey Rublev and Taylor Fritz were among the other seeds to win through on Thursday.