Doha, Qatar , 23 February 2023 | AAP

Chris O’Connell has pulled off one of the best wins of his career at the Qatar Open in Doha.

The Sydneysider  outlasted Spanish luminary Roberto Bautista Agut at the high-quality ATP 250 tournament, battling back from the brink of defeat to earn an exceptional 3-6 7-6(5) 6-4 win in the round of 16.

It was the 29-year-old’s best victory since he defeated the then world No.13 Diego Schwartzman in one of the shocks of the tournament at last year’s Australian Open.

Bautista Agut has dropped to No.28 in the world but the 34-year-old remains a tough nut to crack and it appeared he was going to record a hard-fought but relatively straightforward win as he served for the match in the second set at 5-4.

But world No.94 O’Connell broke back, survived a couple of break points of his own in the next game and took the marathon set into a tiebreak, which he largely controlled.

In the decider, Bautista Agut looked to have weathered an early storm after going 2-0 down and earning a quick break-back, but O’Connell eventually earned the decisive breakthrough in the ninth game, before serving out for victory after a gruelling two hours 39 minutes.

It set up a quarter-final tie with former world No.1 Daniil Medvedev, who defeated Britain’s Liam Broady in straight sets, 6-4 6-3.

Earlier, O’Connell’s compatriot Jason Kubler had been unable to reprise the best win of his career over Felix Auger-Aliassime.

Former world junior No.1 Kubler’s dramatic rise last year had been highlighted by his first-ever victory over a top-10 player when he defeated the No.9 Auger-Aliassime at the Newport Open last July.

But in his first ATP main-tour tournament since lifting the Australian Open doubles crown with Rinky Hijikata in January, the chance of the Queenslander repeating his win over Auger-Aliassime in the last 16 disappeared after Kubler had raced into a one-set lead in the Qatari capital.

The world No.9 Canadian eventually prevailed 4-6 6-1 6-4 in just over two-and-a-quarter hours.

Kubler’s ranking still looks poised to rise again from his career-best No.74 after he beat Aslan Karatsev, who had to withdraw with injury when a set down, in the first round.