After losing in the qualifying rounds in 2016 the Latvian is now just two matches away from claiming her first title since 2010.
Wang, who is the first Chinese player to advance to the quarter-finals since Li Na in 2010, fought off two break points in the opening game and then broke to love to lead 3-1.
She was, however, unable to maintain her advantage as Sevastova immediately broke back and then broke again to lead 5-4 before serving out for the set.
Sevastova continued to hold the upper hand in the second set, breaking to lead 2-1, and although she failed to serve out for the match at 5-4 she broke again for 6-5 and this time finished the job to win 6-4 7-5.
“I think I mixed up pretty well against her,” said Sevastova, who last season at the US Open became the first player from her country to reach the quarter-finals of a Grand Slam since Larisa Neiland contested the Wimbledon quarters in 1994.
“I mean, she’s very solid. She started very well, but I got into my game. I started mixing it up with some stops, some lobs, just not giving her this rhythm, like every time hitting cross, cross, cross. And I think that was the key. Yeah, I returned pretty well too, I think.”
