Almost a year since her last Top 10 win - incidentally which came against Sabalenka in Guadalajara - Samsonova's 7-6, 4-6, 6-4 win in Montreal lasted seven minutes short of three hours and it was worth the wait. Last night, Sabalenka had seen her hopes of overtaking Iga Swiatek in the rankings dissipate.
And the Belarusian has been hit with a double whammy this afternoon after an early exit. Even in the midst of her career-best season, Sabalenka is still prone to occasional losses before the quarterfinals. But all credit must go to Samsonova who was the efficient shotmaker in a battle between two of the WTA's heavyweights.
The first two sets crossed the hour mark and featured a host of long rallies and games. Liudmila Samsonova chose to receive after winning the toss before the start of the match. But she managed to wriggle away through her service games despite Sabalenka's best efforts to exert scoreboard pressure.
Sabalenka paid a hefty price for failure to convert any of her four break points during the first set. On the balance of play, Samsonova deserved to take it into a tiebreak, having fired more winners than the hyper-aggressive Sabalenka. And in the tiebreak, Samsonova nudged ahead after a slow start before sealing the breaker 7-2.
There was a swift response by Sabalenka at the start of the second set, manufacturing a couple more break points in the fifth game, and this time, Samsonova blinked as the double fault count piled up. With the lead, Sabalenka was able to fend off two break points on her own serve in the next game to establish some daylight on the scoreboard.
Samsonova didn't let Sabalenka off the hook and created another break point in the eighth game. But Sabalenka's serve held up firmly in the wake of measured aggression by the Russian before sealing the set in the next service game.
The clock ticked past the two-hour mark when the third set began. Momentum ebbed and flowed. It looked like Samsonova had the match in the bag, but despite breaking Sabalenka for a 3-1 lead, she relinquished her advantage at 4-3.
However, it was only a momentary lapse. In the eighth game of the decider, Sabalenka gifted Samsonova a precious break of serve on a tea tray, serving three double faults in one game. The 15th-seeded Russian stumbled while serving for the match, needing two bites of the cherry before finally finishing off the second seed with a wonderfully controlled drop shot. Samsonova will face Belinda Bencic in the quarterfinal during the night session.