The 18-year-old German, who also reached the quarter-finals in Montpellier last week, trailed in the third set and took it into a tiebreaker where he finally prevailed over Simon, a three-time semi-finalist in the Dutch city.

"The crowd helped me so much," Zverev said. "I really had to give it all I've got. When I was cramping, my team was worried, but I fought hard and stayed in there. Gilles can run all day long so it was tough for me physically."

World number 70 Zverev, who can become the youngest player in the top 100 should he win the title on Sunday, will face France's Gael Monfils on Friday for a semi-final spot.

Sixth seed Roberto Bautista Agut reached his second straight quarter-final and third of the season with a 4-6, 6-2, 6-4 defeat of Jiri Vesely.

The Spaniard, who won the Sofia title last week after also triumphing in Auckland in January, claimed his sixth consecutive victory.

"I'm really pleased with today, I started really badly. Maybe I was tired, I've played a lot of matches this year," said Bautista Agut.

"It took me a while to get into the rhythm. But I got it and started playing very well. I tried to focus on my game, what I could do."

Bautista Agut, the world number 17, will next play Slovak Martin Klizan, who defeated Cypriot crowd-pleaser Marcos Baghdatis 6-3, 6-2. 

Klizan hammered 22 winners and broke five times.

"The start was difficult, we both lost our first service game, but I'm happy I was able to keep my game after that," said Klizan, who could not play the 2013 Rotterdam final due to a foot injury.

French qualifier Nicolas Mahut defeated compatriot Jeremy Chardy 7-5, 6-2 to advance.

The 34-year-old, who has played four matches this week at the Ahoy stadium, will be competing in his second quarter-final of the season after advancing into the top eight last month in Sydney, where he lost to Serb Viktor Troicki.

A repeat of that match will be played on Friday after eighth seed Troicki put out South Korea's Hyeon Chung 7-6 (7/5), 6-2.

The Serb, who turned 30 on Wednesday after playing the weekend Sofia final against Bautista Agut, tamed the 19-year-old tipped as a possible future breakout player.

Troicki advanced with seven aces in 90 minutes.

"He was a very tricky opponent," he said. "He's a young player, I didn't know what to expect.

"I had to play my best to beat him. But I kept focus when I was down, I kept fighting and playing good tennis, I'm pleased to be through."

Mahut, the world number 54, had not defeated Chardy in any of their three previous meetings.

But on Thursday he advanced in just under 90 minutes, overcoming nine Chardy aces and saving all of the seven break points he faced.