Rybakina arrived for the clash after victories over Amanda Anisimova and Iga Swiatek but the former Wimbledon champion came under pressure against a fresh Alexandrova, before breaking in the ninth game and then claiming the opening set with a hold.
The Kazakh, who staved off three breakpoints in the first set, cranked up her big serve and heavy hitting early in the second to go 3-1 up and applied the squeeze to close in on another win ahead of the semi-finals.
Another break courtesy of a powerful return of serve left Rybakina one game away and the 26-year-old eventually wrapped up the victory despite some struggles on her own delivery late in the clash at King Saud University Sports Arena.
Swiatek and Anisimova meet later on Wednesday in a winner-takes-all match to decide who joins Rybakina in the last four as the second-best player from the Serena Williams Group at the end of the round robin stage.
It will be their third meeting this season, with Swiatek having crushed Anisimova 6-0 6-0 in the Wimbledon final in July to claim her first All England Club title before the American gained revenge in the U.S. Open quarter-finals in September.
Keys withdraws
Madison Keys has withdrawn from her WTA Finals clash against Elena Rybakina on Wednesday due to a viral illness and has been replaced in the draw by Ekaterina Alexandrova.
The Australian Open champion suffered two defeats in round-robin play this week in Riyadh, to Swiatek and Anisimova, and had no chance of advancing to Friday’s semi-finals.
At the end of her match against Anisimova on Monday, Keys wouldn’t shake her opponent’s hand, indicating she was feeling unwell and didn’t want to pass on the virus.
“I’m really disappointed to not be feeling my best and ultimately having to withdraw from the tournament. It’s a huge accomplishment to make it this far and I’m very proud of myself for doing that and having a great year. I hope to be back next year,” said Keys in a statement.
Alexandrova is the second alternate in Riyadh. The first alternate, Mirra Andreeva, who is already competing in the doubles at this year’s WTA Finals, elected not to sign in due to not being fit to play on Wednesday.
Andreeva has a doubles match on Thursday, alongside her partner Diana Shnaider, and might be called in for duty as an alternate to replace Jasmine Paolini in singles, given the Italian is no longer in contention for a semi-final spot and is also feeling unwell.
Wednesday’s schedule features the third and final set of round-robin matches in the Serena Williams Group, with Rybakina taking on
Alexandrova and Swiatek facing off with Anisimova.
Rybakina has already secured her place in the semi-finals as the group winner, while Swiatek and Anisimova will battle it out for the other ticket to the final four.