Jo-Wilfried Tsonga marked his return from injury at the Shanghai Masters with a comfortable first-round win over Florian Mayer.

The world number 13 had not played since being forced to retire from his US Open quarter-final with Novak Djokovic with a knee issue.

But he showed little signs of rust on Monday as he saw off Mayer 6-3 6-2 in just 71 minutes.

Tsonga was the only seed in action in Shanghai, but teenager Alexander Zverev provided a further demonstration of his talent with a straight sets win over John Isner.

Steve Johnson also progressed, but Ivo Karlovic is out of the ATP 1000 event after defeat to Vasek Pospisil.

TSONGA MAKES SHORT WORK OF MAYER

Tsonga went into his meeting with Mayer having won all five of their previous encounters.

And the German was unable to end his wait for a victory against the former Australian Open finalist as he paid the price for wasting two break points in the opening game of the match.

The Frenchman took full control after winning the opening set and, though Mayer fought hard to save four match points, his effort proved in vain as the ninth seed set up a clash with Janko Tipsarevic.

ZVEREV ZOOMS INTO ROUND TWO

With just five places separating the two in the rankings, Zverev's contest with Isner looked set to be a hard-fought one.

But that did not prove the case as the 19-year-old German showed why he sits above the American in the rankings, the world number 21 winning 6-4 6-2.

Known for his booming serve, Isner found himself behind on the ace-count 9-5, with both players losing just seven points on their first serve. However, Isner won only seven points on his second serve and was punished as Zverev broke four times.

JOHNSON BOOKS MURRAY MATCH, KARLOVIC CRASHES OUT

Johnson narrowly missed out on beating Andy Murray in the quarter-finals at Rio 2016, but will have a chance to avenge his Olympic loss after seeing off Martin Klizan 6-4 6-3.

The American required only 61 minutes to end the Slovakian's challenge, and will now aim to dent Murray's bid to end the year as world number one.

But Karlovic's tournament is over despite the Croatian sending down 14 aces against Pospisil, the Canadian coming through to face Grigor Dimitrov or Richard Gasquet.

MEANWHILE...

Viktor Troicki is also into round two following a routine 6-2 6-4 triumph against qualifier Lukas Rosol, but Joao Sousa is out after going down 6-3 5-7 6-1 to Benoit Paire.

There were also three-set wins for Kyle Edmund, Nicolas Almagro, and Taylor Fritz while Mischa Zverev overcame Zhang Ze in straight sets.