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 in the first set.

“It was really close. It could have gone both ways. The key was to stay there at 5-2 [in the tie-break]. I played five great points in a row.”

The world No 24 has now won eight of his past nine ATP tour matches and set up a third-round meeting with France’s Luca Van Assche.

Musetti, a two-time grand slam semi-finalist, landed 29 winners and eight aces over the course of an hour and 40 minutes at Paris’ La Defense Arena.

Defeat for Zverev means the German has gone two seasons without a Masters title, with his last coming in Paris in 2024.

Earlier on Wednesday Arthur Fils booked his place at the ATP Finals for the first time, becoming the first Frenchman to compete at the year-end tournament in 10 years - the last being Gael Monfils, who retired in a special ceremony in Paris this week.