Andy Murray waits for 700th career win after defeat to Jannik Sinner in Dubai
Scotland’s three-time grand slam winner battled well in the first set but was outplayed in the second, beaten 7-5 6-2 by one of the rising stars of the men's game.
The first set went efficiently to serve from both ends until Sinner struck, breaking 2017 Dubai winner Murray to love for 6-5.
Murray got to 30-30 in the 12th game, but a mighty Sinner first serve and a stunning forehand winner later and the set had slipped away.
Sinner, already ranked 10 in the world at the age of 20, broke again with ease at the start of the second and Murray had to save two break points just to get on the board at 1-2.
However, with Sinner coming forward aggressively and putting Murray away at every opportunity, the 34-year-old won just one more game to bow out in round two.
Murray got win number 699 after coming from a set down to beat Christopher O'Connell in the previous round, yet blamed a lack of mental toughness for falling short of his latest milestone on this occasion.
He said in his post-match press conference: "Obviously it's something I want to achieve.
"Unless something went horribly wrong in the next six, eight months, I will get to that number. But, yeah, there's no excuse for some of the performances I've had recently in terms of how I've been playing.
"I need time on the practice court. I need consistency in terms of the things that I'm working on, consistent messages.
"Yeah, I mentally need to be a lot tougher than what I have been in some of my matches recently."
Murray also confirmed he would announce a short-term coach to take him through to the grass season in the coming days.
Meanwhile, world number three Alexander Zverev has been booted out of the Mexican Open after repeatedly smashing an umpire's chair with his racket following after the German and Brazilian partner Marcelo Melo were beaten 6-2 4-6 10-6 by Britain's Lloyd Glasspool and Finland's Harri Heliovaara in the doubles.
Tournament organisers confirmed that Zverev was being withdrawn from the event due to “unsportsmanlike conduct” and his second-round opponent in the singles, Peter Gojowczyk, has been given a walkover.
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