Nadal through to last-16 in Rome after Almagro injury

( Reuters) - Rafael Nadal eased into the last-16 of the Italian Open on Tuesday when his second-round opponent Nicolas Almagro retired after sustaining a knee injury early in the first set.

Nadal, who is the clear tournament favourite and looks to be back to his best form on clay this season, raced into a 3-0 lead before Spanish compatriot Almagro felt his left knee with less than half an hour played.

Nadal is seeded fourth in Rome, where he is bidding for a record eighth title to go with his recent successes in Monte Carlo, Barcelona and Madrid, and will meet either American Jack Sock in the next round after he beat Jiri Vesely.

Japan's Kei Nishikori, the number seven seed, beat Spaniard David Ferrer 7-5 6-2 earlier in the day and will face Argentina's Juan Martin del Potro in the last 16.

Third seed Stan Wawrinka avenged his defeat by unpredictable Frenchman Benoit Paire in Madrid last week when the 2015 French Open champion won a topsy-turvy match 6-3 1-6 6-3.

Austrian dark horse Dominic Thiem, runner-up to Nadal in Madrid, beat Pablo Cuevas 7-6(4) 6-4 to line up a last-16 clash against big-serving American Sam Querrey.

(Reporting by Simon Jennings in Bengaluru; editing by Mark Heinrich)