China's Xu Si battles back to upset Mark Williams at Xi'an Grand Prix

Chinese snooker player Xu Si continued his impressive streak by defeating three-time world champion Mark Williams 5-4 in the round of 16 at the Xi'an Grand Prix on Thursday.

Xu had just come off a grueling nine-frame battle in the previous round that saw him eliminate former world champion Stuart Bingham of England.

Against Williams, he found himself trailing 4-2 after six frames. But the Welshman made several unforced errors in the seventh frame, showing signs of fatigue and loss of focus, while Xu seemed to grew stronger as the match progressed.

In the deciding frame, Xu compiled a century break to secure the victory, becoming the only Chinese player to advance to the quarterfinals. He will next face England's reigning world champion Kyren Wilson.

In other action, Xu's compatriot Gong Chenzhi suffered a heart-wrenching 5-4 defeat against Matt Selt. Gong had impressed in Xi'an with victories over Tom Ford and Si Jiahui, positioning himself well for a potential place in the quarterfinals. But the English veteran Selt staged a stirring comeback, winning the crucial penultimate frame on the black ball, before clinching the decider.

Meanwhile, Ronnie O'Sullivan enjoyed a smooth 5-0 win over Hossein Vafaei, breezing past his old rival from Iran. England's "Rocket" has been dominant at this tournament, defeating Wang Yuchen, Bulcsu Revesz, Yuan Sijun and now Vafaei with an aggregate frame score of 20-3. Selt awaits O'Sullivan in the quarterfinals.

Another title favorite, Judd Trump, also reached quarterfinals after securing a 5-1 win over Jak Jones of Wales to send the "Juddernaut" into a last-eight meeting with fellow Englishman David Gilbert.