Garbine Muguruza squandered three match points as she was stunned by Daria Kasatkina in the semi-final of the Dubai Tennis Championships.
Muguruza came into the tournament on the back of an excellent performance at the Qatar Open, where she lost a thrilling final to Petra Kvitova.
But her hopes of a second successive final appearance were ended by world number 24 Kasatkina, who looked poised for defeat in the second set tie-break, only to frustrate Muguruza and then race away in the decider to a 3-6 7-6 (13-11) 6-1 win.
Kasatkina's heroics were something of a repeat of her last-16 performance, which saw her save two match points en route to defeating Johanna Konta.
After winning the opening set, a frenetic second that featured four breaks appeared poised to go the way of Wimbledon champion Muguruza, who saw off two Kasatkina set points in the tie-break, only to see the Russian hold firm and deny her at 8-7, 9-8 and 10-9.
The 20-year-old then needed just 30 minutes to wrap up the third as Muguruza never recovered, Kasatkina claiming her first win over the Spaniard in three attempts, having lost to her in a decisive tie-break in Brisbane last year.
Kasatkina, who will move into the world's top 20 regardless of what happens in the final, said: "The fighting spirit made the difference. I was just trying to fight for every ball because Garbine, she's playing unbelievable. She's very tough opponent. She's hitting so hard, playing so fast. I was just trying to do whatever I could."
The final will see Kasatkina attempt to win only her second WTA title against defending champion Elina Svitolina, who saw off former world number one Angelique Kerber 6-3 6-3, marking her fifth successive victory over the German.
"I'm very pleased with the performance," Svitolina said. "I was very happy with the way I played in the top moments."
On Kasatkina, she added: "She plays well, she had tough matches. It's definitely going to be a good final."
Meanwhile, at the Hungarian Open, top seed Dominika Cibulkova eased into the semi-finals with a 6-3 6-2 victory over Johanna Larsson. Mona Barthel is next for Cibulkova after her defeat of Ysaline Bonaventure.
Viktoria Kuzmova is also into the last four after beating Petra Martic, with Alison van Uytvanck her opponent, the Belgian overcoming Zhang Shuai in straight sets.
|Jason Day hungry to reclaim top ranking: My game is close|
|Iconic 2002 World Cup haircut was media distraction, reveals Ronaldo|
|New Zealand star Taylor fit for day-night Test|
|Teenager Anisimova to face Muguruza in Miami|
|McIlroy credits Wayne Rooney for improved putting|
|Stokes return a ´huge boost´ for England – Root|
|Wright: Difficult for Liverpool sensation Salah to resist Real Madrid|
|Yaya Toure yet to report for international duty, confirm Ivory Coast|
|Masters favouritism could hinder Woods, Thomas claims|
|I wish I could still play with him – Ortiz on Red Sox addition Martinez|
|Morrison confirms plans to play for Jamaica|
|Warriors target Friday return for Curry against Hawks|
|Starc and Marsh set to play at Newlands|
|Red alert: Richard Sherman ´excited´ to be a 49er|
|Germany should be proud to have Sane, says Tah|
|Bertrand out of England friendlies with back injury|
|Optimistic McIlroy ´crossed that line´ with Bay Hill win|
|Young backs Mourinho over Shaw treatment|
|BVBolt? Athletics great scores header while training in Dortmund kit|
|Fekir will look to leave Lyon the right way, says agent|
|Ex-Springboks coach Meyer takes charge at Stade|
|Spieth relishing Reed match play showdown|
|Alisson loves Roma and we haven´t discussed Liverpool move, insists agent|
|Henderson becomes third Ireland player to sign new deal|
|Romo ready to create ´mental bubble´ ahead of PGA Tour debut|
|McTominay: I always wanted to play for Scotland|
|Chiesa vows to honour Astori with Italy displays|
|England´s Pope ready for Heaton challenge amid World Cup race|
|Lautaro Martinez confirms impending Inter move|
|Morata wasn´t happy with Spain snub, admits Alonso|
|Raiola rages over Italy´s Balotelli snub|
|Injured Saunders postpones Murray fight|
|PGA tightens security at Dell Match Play in wake of Austin bombings|
|Raiola hopes Reina to Milan hastens Donnarumma exit|
|F1 Raceweek: Hamilton prepares to begin title defence in Melbourne|
|Former Sevilla coach Berizzo eyeing return after beating cancer|
|Cutrone did not expect whirlwind Milan season and Italy call-up|
|Saints punish North for missing training|
|´Happy´ Kepa mulled over Real Madrid move|
|GGG wants Saunders next if Alvarez bout is called off|
|Former All Black Mika passes away|
|Lucas Vazquez keen on Real Madrid stay|
|South Africa delighted to call on ´world´s best´ Rabada|
|Tiger Woods continues climb in FedEx Cup, world rankings|
|Juventus clear Chiellini of serious injury|
|Newcastle charged as youth team allegedly breach advertising regulations|
|Kearney joins Best in extending Ireland contract|
|I did not betray Roma – Pjanic could not pass up Juventus opportunity|
|Cardiff Blues appoint Mulvihill as Wilson replacement|
|Title-chasing Sarri closes on Napoli renewal as he hopes to repay fans|
|Cook: I wasn´t close to quitting during Ashes|
|Messi and Ronaldo reveal World Cup kits|
|Nara praises Inter project as Icardi talks continue|
|Best to lead Ireland in World Cup after signing extension|
|Marseille´s Rami wants to ´tickle´ PSG|
|Fury targeting Louis´ record for title defences|
|Salah can push on to Messi´s level - Robertson|
|Rabada free to play in rest of South Africa-Australia series|
|F1 2018: Halo splits opinion ahead of Australia debut|
|Iniesta better than last year – Lopetegui|
|Federer yet to decide on clay-court season|
|Okon quits as Mariners head coach|
|LeBron triple-double powers Cavs past Bucks as Love returns|
|Lopetegui: Morata must earn World Cup spot|
|Ronaldo has asked about China – Scolari|
|Ebron signs two-year deal with Colts|
|Spieth, Reed to do battle in Match Play|
|Rangers´ Perez slaughtered, ate bull that caused broken elbow|
|Bills improve offensive line with Bodine, Newhouse|
|Braves phenom Acuna to start season in minors|