Memphis - Top seed Marin Cilic saved three match points en route to a 7-6 (7/2), 3-6, 7-6 (9/7) victory over Igor Sijsling on Thursday to book a quarter-final berth in the US Indoor Tennis Championships.
Croatia's Cilic trailed 4-6 and then 6-7 in the third-set tiebreaker, but won the final three points to take the match from his Dutch foe.
Cilic next faces Japanese fifth seed Kei Nishikori, who beat qualifier Donald Young 6-3, 6-3.
World number 63 Denis Istomin reached his fourth ATP quarter-final of the season, beating Australian veteran Lleyton Hewitt 6-1, 6-2.
Istomin next faces lucky loser Michael Russell, who beat Lukasz Kubot of Poland 6-2, 6-4.
In women's action in this $1.58 million combined ATP and WTA event, top seed Kirsten Flipkens fell prey in the quarter-finals to the upset bug that saw second-seeded Sofia Arvidsson ousted in the second round.
Seventh-seeded Slovak Magdalena Rybarikova, the winner of this title two years ago, defeated Flipkens 6-7 (11/13), 7-5, 6-3.
In the semi-finals, Rybarikova will take on third-seeded German Sabine Lisicki, who cruised past eighth-seeded Kristina Mladenovic of France 6-3, 6-3.
The other semi-final will pit Switzerland's Stefanie Vogele against Marina Erakovic.
Vogele defeated fourth-seeded Briton Heather Watson 6-1, 6-2, and New Zealand's Erakovic beat American Jamie Hampton 7-5, 6-2.