James Duckworth has gone out of the St Petersburg Open, beaten in straight sets by Jan-Lennard Struff in the tournament's opening match.

Struff, who at No.53 is ranked two places below Duckworth, took one hour and 45 minutes to win the pair's first meeting 7-6 (7-3) 6-3.

Having broken his German opponent's first service game, Duckworth led 5-2 and served for the set at 5-3 but was unable to close it out.

In the tiebreaker the Australian No.2 established a mini-break to grab a 2-1 advantage but failed to win another point on serve to go a set down.

The second stanza turned on Duckworth's second service game, which lasted 25 points.

He saved five break points, one with an 205km/h ace, but missed six chances to secure the game before Struff prevailed.

Duckworth saved three match points before Struff sealed the result.

The Sydneysider has reached a career-high 51st in the rankings off the back of reaching his maiden final on tour in Nur-Sultan, Kazakhstan, last month.

John Millman will face Israeli wildcard Yshai Oliel in his first-round match.

Meanwhile, American Sebastian Korda advanced to the second round with a 7-6 (7-2) 7-5 win over Nino Serdarusic to set up a showdown with third-seeded Roberto Bautista Agut.

Seventh-seeded Alexander Bublik progressed with a 6-3 6-4 win over unfancied Russian Evgenii Tiurnev.