Auckland, New Zealand (SportsNetwork.com) - Two-time NCAA singles champion Steve Johnson posted an opening-round win Monday at the Heineken Open tennis event, a final Australian Open tune-up.

The eighth-seeded American took care of Portuguese Joao Sousa 7-5, 6-4 on the hardcourts at ASB Tennis Centre.

Also on Day 1, German Jan-Lennard Struff overcame Austrian Dominic Thiem 6-7 (6-8), 6-4, 6-3 and France's Adrian Mannarino drilled Argentine Federico Delbonis 6-1, 6-1.

This week's top seeds are Spaniard Tommy Robredo and Latvian Ernests Gulbis. Two-time winner John Isner, who is not defending his title this week, beat Taiwan's Yen-Hsun Lu in last year's Auckland finale.

The 2015 Auckland champ will pocket $84,500.