"It was tough, I just hung in at the end and got through," unseeded Evans said. "But I just didn't fancy playing another set. I think that's what got me through."
Tsitsipas trailed throughout most of the match against the 34th-ranked Struff, only taking the statistical lead late in the third set with a break for 5-4 which set up his victory. "I was struggling with my return today, I don't know what was wrong with it," Tsitsipas said.
"I couldn't really find enough space to get that right momentum to hit the ball, that was the biggest struggle today. "I'm actually pretty proud that I fought so hard, played with attention when I had to. When I got the break in the third set I knew that was my time to close the match now. I did it in perfect style."
Tsitsipas is defending his runners-up points from last year when he lost the final to Roger Federer. He arrived in Dubai after winning the Marseille trophy at the weekend. Struff reached the quarters after spending just 39 minutes in winning his previous match.
Top seed Novak Djokovic was playing his quarter-final later Thursday against Russian Karen Khachanov while number three Gael Monfils was squaring off with French compatriot Richard Gasquet. Evans, 29, whose previous last four semi-final appearances came in Zagreb in 2014, Sydney in 2017 and Delray Beach a year ago, needed nearly two and a quarter hours to advance.