National shuttler Yeo Jia Min's first thought upon becoming the first Singapore woman to reach the singles quarter-finals of the BWF World Championships was one of relief.

The 20-year-old, who sank to her knees and closed her eyes after converting her fourth match point to end a gruelling 72-minute battle yesterday, said: "I felt relieved because I was determined to win."

The world No. 32 had to overcome discomfort in her lower back to beat Vietnamese Vu Thi Trang 21-15, 14-21, 21-16 at St Jakobshalle in Basel, Switzerland.

While she advanced, fellow Singaporean Loh Kean Yew failed in his bid to reach the last eight after a 13-21, 21-18, 17-21 loss to men's world No. 2 Chou Tien-chen of Chinese Taipei.

Yeo won the first game in 20 minutes, often getting the better of her 74th-ranked opponent in long rallies.

The Vietnamese then raised her tempo in the second game and injected more pace into her shots as Yeo fumbled.

The Singaporean regrouped to take the lead in the third game as she put pressure on Trang's forehand.

Though her rival fought to save three match points, Yeo held steady and closed out the win.

She was constantly referred to as a giant-killer by commentators yesterday following her shock second-round win over world No. 1 Akane Yamaguchi of Japan on Tuesday.

But Yeo felt no pressure during her match against Trang, saying of the four match points: "I felt collected and focused on the match, and reminded myself of things I could control.

"I feel happy and excited to enter the quarter-finals."

Today, the former junior world No. 1 will face 2013 world champion and world No. 6 Ratchanok Intanon of Thailand, who beat Indonesian Gregoria Mariska Tunjung 18-21, 23-21, 21-10.

Yeo said: "I will focus on recovery and preparing my (mind) for the (last eight) match."

Her compatriot Loh, the world No. 34 who won his last two matches after dropping the first game, was denied a third straight comeback win in his third-round match.

After losing the first game in 16 minutes, he adopted a more aggressive tactic to force a third game.

The decider saw several shifts in momentum, with the 22-year-old Singaporean leading 6-3 before a fired-up Chou won five straight points to edge ahead and later go up 18-11.

Loh then took the next six points and saved the first match point before Chou sealed the victory.

The Singaporean admitted he could have played better in the third game, noting: "(Chou) suddenly increased his speed, which caught me off guard and I took too long to (adapt) and overcome his strategy."

Despite the loss, he was happy with his outing. "I'm glad that I can watch and play with top players, and also gauge my standard with them," he said.

Ronald Susilo was the last Singaporean man to reach the world tournament's quarter-finals in 2007.