Murray tested by Mayer in Valencia second round

Andy Murray of Britain reacts after losing a point in his match against Marin Cilic of Croatia at the U.S. Open tennis championship in New York, September 8, 2009. Cilic won the match.

VALENCIA, Spain (Reuters) - Top seed Andy Murray beat little-known Argentine Leonardo Mayer 6-4 3-6 6-3 in the second round of the Valencia Open on Thursday as the Briton continued his comeback from a wrist injury.

The world number four, who before this week had not played on the ATP tour since September's U.S. Open, will play Spaniard Albert Montanes on Friday for a place in the last four.

Second seed Nikolay Davydenko made smooth progress in his bid for a place at the season-ending World Tour Finals in London later this month with a 6-3 7-5 second-round win over Juan Monaco of Argentina.

The Russian conceded two breaks of serve but broke Monaco four times to set up a quarter-final on Friday against Guillermo Garcia-Lopez of Spain.

Roger Federer, Rafael Nadal, Novak Djokovic, Andy Murray, Juan Martin del Potro and Andy Roddick have all qualified for the November 22-29 Tour Finals and Davydenko and Valencia fourth seed Fernando Verdasco occupy the remaining two spots.

Spaniard Verdasco advanced in Valencia with a 6-3 6-3 win over Janko Tipsarevic of Serbia and will play compatriot Tommy Robredo in the last eight.

Seventh seed Robredo, who has an outside chance of a Tour Finals spot, came from a set down to beat Feliciano Lopez, another Spaniard, 4-6 6-3 6-4.

Russian Mikhail Youzhny went through to the quarters thanks to a 6-2 2-6 6-1 victory over Uruguayan Pablo Cuevas and next plays London hopeful and fifth seed Gilles Simon of France.

David Ferrer's slim hopes of a spot in London ended when a hamstring injury forced him to withdraw from his second-round match against fellow Spaniard Montanes before a ball was struck.

(Writing by Iain Rogers in Madrid; editing by Pritha Sarkar)