ASB Classic: Top seed John Isner upset in opening round by Taylor Fritz

The ASB Classic has lost another of its main drawcards after number one seed John Isner was ousted in the opening round by compatriot Taylor Fritz.

The unseeded Fritz earned an unlikely 7-6, 7-6 straight sets win to bundle world number 10 Isner out of the tournament on day three.

Isner has been a mainstay in Auckland in recent years, and was crowned champion in both 2010 and 2014. 

His departure further depletes the star power on offer at the tournament, with rising star Hyeong Chun's first-round upset loss to Kiwi Rubin Statham, and the late withdrawls of Gael Monfils, Tomas Berdych and defending champion Roberto Bautista Agut.

New Zealand-raised Briton Cameron Norrie also progressed, ousting Joao Sousa 7-6, 6-4.

Earlier, Italian Fabio Fognini narrowly avoided befalling the same fate as his fellow seeds as he prevailed over Germany's Peter Gojowcyzk 2-6, 6-3,7-6 in a hard-fought contest.

The tournament's other remaining seed, Pablo Carreno Busta, will take on fellow Spaniard David Ferrer in Wednesday's night session.

In other action, USA's Tennys Sandgren beat Marco Cecchinato 6-3, 6-3 to advance to round three after his first-round bye.