Displaying brilliant tennis against his young opponent in the finals, Monfils cruises to a 6-2, 6-3 in Doha.
The 39th-ranked Rublev has had trouble with his serve throughout the tournament. "Maybe I wasn't focused at times".
Gael Monfils wins his seventh career ATP singles title. As a lucky loser, Rublev won his first career title, in his first career final, at the Umag, Croatia tournament a year ago.
Number one seed and world number five, Austria's Dominic Thiem plays later against another highly-rated youngster, Stefanos Tsitsipas.More news: Amit Shah sounds poll bugle in Meghalaya
Thiem hit two forehand winners from 15-30 to break Tsitsipas' serve in the ninth game of the second set and saved a break point in the 10th before securing his place in the semi-finals. "Of course I am disappointed, but nevertheless I had a solid start into the new season", the Austrian wrote on his official Facebook account.
"It was in 2016 I was nearly on top and I had a very good year, finished sixth, and couldn't really defend my chances in 2017", added Monfils. To me it happened when I had to close out the (first) set.
Thiem showed signs of illness when he coughed through numerous answers during his quarterfinal post-match press conference on Thursday night.
Gael Monfils is the 2018 Qatar Open champion in men's singles. "Now I am focusing on Melbourne and being fit and prepared for the first Grand Slam of the year", Thiem said. "I'm just pleased the way that the year start and I'll be ready for tomorrow".