Rafael Nadal took advantage of an error-strewn display from Stan Wawrinka to begin the ATP World Tour Finals with a straight-sets victory on Monday.
Nadal has endured a difficult year in which he has failed to progressed beyond the quarter-finals of a grand slam, but his form towards the end of 2015 has been far more encouraging - as Wawrinka discovered at the O2 Arena.
The Spaniard won 6-3 6-2 in the second match on day two of the tournament to join Andy Murray - who beat David Ferrer in straight sets - at the top of the Ilie Nastase Group.
Fourth seed Wawrinka has won four titles this year - including the French Open - but failed to meet the high standards he has set in his first clash of the tournament in London, making 35 unforced errors and paying the price.
Wawrinka broke to love in style in the opening game by unleashing a rocket of a cross-court backhand, but Nadal hit straight back by winning all four points on the Swiss' serve in a strange start.
Nadal piled on the pressure in the eighth game and Wawrinka was unable to withstand it as he overcooked a forehand to go 5-3 down, allowing the fifth seed to serve out the set with a booming ace.
An increasingly frustrated Wawrinka dug deep for the hold after saving seven break points in the first game of the second set, but Nadal produced an exquisite lob as he fended off break points before being gifted a 2-1 lead when his struggling opponent double-faulted.
Wawrinka then sent a backhand long to go a double-break down at 4-1 and there was no way back for the deflated two-time grand slam champion, as Nadal gave himself a great chance of reaching the semi-finals.
Nadal  bt Wawrinka  6-3 6-2
Nadal - 10
Wawrinka - 1
BREAK POINTS WON
Nadal - 4/15
Wawrinka - 1/3
FIRST SERVE PERCENTAGE
Nadal - 61
Wawrinka - 60
PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Nadal - 70
Wawrinka - 53