"It's been a while since I had a big win like today," said the 30-year-old Greek, who reached No. 3 in the rankings in 2022 but has slipped to 52nd.

"When you drop in the rankings and you're not playing good tennis you start doubting yourself and you think you are never going to beat those players again. So it's a huge process ou have to go trough in your head that you can do it."

Sakkari won her first three career meetings with the young Swiatek but the last of those victories came in 2021. The Pole had won their last four matches, the most recent in straight sets in Qatar last year.

"Last year here in the second round here against her, I was not confident, I was not believing in myself and this year it's different. I feel a lot better," said Sakkari.

Swiatek, who won the Qatar tournament, a  WTA 1000 event, in 2022, 2023 and 2024, started as if she would repeat last year's rout when she broke twice in the first set.

Sakkari began to fight back in the last game, but Swiatek saved a break point to seal the set.

Sakkari continued her upswing by breaking in the second game of the second set.

Yet every time she gained an edge, Swiatek responded. The Pole broke in the seventh game, but Sakkari steadied and  broke in the tenth game to take the set.

It was the first time in their seven meetings that a match between the pair had gone to a third set.

In the deciding set, Sakkari broke in the fourth game. Swiatek broke back at once only for Sakkari to break again immediately.

In the seventh game Sakkari saved two break points but Swiatek took a hard-fought ninth, on a third break point.

Swiatek saved a match point in the next game but Sakkari then held to love, and won in the next game, on her third match point, when The Pole volleyed  tamely  into the net.

The match lasted one minute under two-and-a-haf hours.

In what will be her fourth Qatar semi-final, Sakkari will face either 14th seeded Czech Karolina Muchova or undeeded Russian Anna Kalinskaya.

"I've missed that feeling of going deep into tournaments," said Sakkari.

In the day's first quarter-final, Latvian Jelena Ostapenko blazed past Italian Elisabetta Cocciaretto 7-5, 6-4 and will face either rising Canadian teenager Victoria Mboko or second seed Elena Rybakina.