Alexander Zverev endured a disappointing start to his first week as world No 1 as he slumped to a straight-sets defeat to Lorenzo Musetti at the Paris Masters .

The German reached the top of the world rankings when they were updated on Monday but lost 7-6(5) 6-2 to the in-form Italian in his first match with his new title, after receiving a bye to the second round of the Masters 1000 event.

29-year-old Zverev led by 5-2 in the first set tie-break before Musetti won six of the last seven points to seal the set, then surged ahead in the second to break for 2-1 and again for a 5-2 lead before serving out victory.

Former world No 5 Musetti has endured a difficult 2026 hampered by injuries, beginning when he led Novak Djokovic by two sets in their Australian Open quarter-final, but has come into a purple patch late in the season, winning his first title in four years in Lyon last month.

Musetti said: “It’s pretty shocking the level I was able to play in front of Sascha, who was serving really well, especially…