BEIJING, China - Anastasija Sevastova has added No.8 seed Naomi Osaka to her list of big-name scalps, reaching the biggest final of her career at the China Open with a 6-4, 6-4 win in one hour and 31 minutes.

It is the fourth Top 10 victory of 2018 for the unseeded Sevastova - the most the Latvian has racked up in a single season - as well as her third defeat of a reigning Grand Slam champion, following her US Open upsets of Garbiñe Muguruza in 2016 and Sloane Stephens this year. It also means that the 28-year-old, a three-time champion and three-time runner-up at International level, progresses to her first ever Premier Mandatory final.

Although the result is an upset both on paper and given the irresistible form of Osaka, who was bidding to become the first player in 2018 to reach three consecutive finals, it is in fact Sevastova's second win over the Japanese player this year, having triumphed 6-4, 6-1 in the second round of Doha in February. The first set saw the Bucharest champion deploying similar tactics, varying the length, depth and spin of her strokes to prevent Osaka getting into her usual thunderous groove.

Although the US Open champion's ability to deal with such tactics has vastly improved this year, as evidenced by her quick reflexes in dealing with a fiendish dropshot in the sixth game, Sevastova was able to elicit errors on several occasions with judicious use of slice - and kept Osaka on her toes with flashes of inspiration, such as a clean slice winner in the fifth game and a casual dropshot return-drive volley combination in the ninth.

Nonetheless, the first set was a tightly contested one that would ultimately be decided by just one break. Osaka would be the first player to be tested, staving off three break points in the third game with strong serving; three games later, Sevastova would save two against her to emerge from a six-deuce tussle. Increasingly plagued by errors, Osaka would promptly offer up two off the forehand and three off the backhand to slip down 4-3.

Perhaps the most crucial - and surprising element - to Sevastova's success today was the efficacy of her serve, particularly compared to Osaka's more renowned delivery. Having hitherto struck just three aces in the tournament, the US Open semifinalist hammered down ??? today, with three coming in one game to aid her epic hold for 3-3 and a sixth sealing the first set at the first opportunity.

By contrast, Osaka - who would require medical treatment on her lower back in the second set - was particularly struggling on second serve, winning just 35% of the points behind it as Sevastova read it perfectly. As the match progressed, the 20-year-old would lapse into a spate of double faults, coughing up four in the second set.

As Sevastova continued to hit her spots, repeatedly wrongfooting her opponent and continuing to serve strongly, a frustrated Osaka began to hit out wildly, dropping her serve with another cascade of errors in the fifth game of the second set. The home stretch would not be plain sailing for the Mallorca finalist, who missed two opportunities to go up a double break for 5-2 and double faulted on a point for 5-3. Finding her range with some big backhands, Osaka threatened a resurgence in a second straight round as she broke back for 4-4.

But even with the World No.20 rattled, the Indian Wells champion was unable to keep the ball in court long enough to take advantage, ultimately tallying 42 unforced errors to outweigh her 24 winners. Another handful of errant backhands, and Sevastova had captured the break lead again. Serving for the match, she would settle herself again, opening with positive play and a backhand winner down the line - her 18th of the day - and take victory on her first match point with an unreturned serve.

Sevastova, who returned to the game in 2015 following a two-year retirement, continues to exceed herself every year since her comeback. In 2016, there was a maiden Grand Slam quarterfinal at the US Open; she ended the following year in the Top 20 for the first time. In 2018, one of the canniest and naturally skilled players on Tour has already added to her resumé with a first major semifinal - and now the biggest final of her career, in which she will face either No.2 seed Caroline Wozniacki or wildcard Wang Qiang.