James Duckworth has stormed home to secure a three-set first-round win over fellow Australian Alexei Popyrin at the ATP event in San Diego.

The seventh seed and world No.83 booked his spot in the round of 16 with a 7-5 4-6 6-1 victory in just shy of two hours 20 minutes on Monday.

The 30-year-old was dominant on serve, blasting down 14 aces and winning 85 per cent of his first balls.

But he made a slow start, world No.90 Popyrin breaking in the opening game and leading 3-1 before Duckworth fought back to take the opening set 7-5 in 50 minutes.

Popyrin levelled the contest in similar time after breaking in the ninth game of the second set before serving it out, but ran out of steam in the decider.

It is Duckworth's third consecutive win against another Aussie, having also beaten Thanasi Kokkinakis and Chris O'Connell in the past month.

Duckworth will face either Christopher Eubanks or Mitchell Krueger - both local qualifiers - as he tries to reach his second tour-level quarter-final of the year, having advanced to the last eight in Newport in July.

In another round-of-32 all-Australian clash, Jason Kubler and O'Connell will meet on Tuesday (Wednesday AEST) with the winner taking on J.J. Wolf after the eighth seed saw off fellow American Stefan Kozlov 6-2 7-6 (8-6).

Tomas Martin Etcheverry won the all-Argentine contest against Facundo Mena 7-6 (8-6) 6-3.

World No.2 Casper Ruud of Norway has not returned to defend his title in California with Brit Daniel Evans, the world No.25, the top seed.