Rafael Nadal made a winning start to his latest bid for a first ATP World Tour Finals title, but was pushed all the way by Mardy Fish in a pulsating late night encounter at the O2 Arena on Sunday.
The Spaniard was taken to three sets by his American opponent before finally prevailing 6-2 3-6 7-6 (7-3) in an encounter which lasted nearly three hours.
The victory means Nadal joins old rival Roger Federer at the top of Group B after the Swiss star's victory over Jo-Wilfried Tsonga earlier in the day.
Nadal appeared set for a rapid success as he took advantage of countless errors from Fish to race through the first set.
The tone was set for the American as he dropped serve in the very first game of the contest and he struggled to find any consistency or rhythm with his groundstrokes.
Nadal secured a double-break after produced two stunning cross-court winners to take a 5-2 lead and duly served out the clinch the first set.
But Fish cut a rejuvenated figure in the second and, having given himself the fillip of an early break, grew into the match with each passing game.
Serving at 2-5, Nadal staved off four set points but, having survived, was then unable to take a break-back point of his own in the next as Fish served out to level up proceedings.
A sublime forehand winner on the run from outside the tramlines gave Nadal a break in the second game of the decider at which point he rushed from the court for an unscheduled break.
Fish seemed initially irked by the Spaniard's disappearing act, but Nadal was quick to apologise on his return and the American did not seem distracted as he produced a perfect drop shot to break straight back.
Fish won another break with a backhand winner from the baseline, but the American was unable to cling on to his advantage and allowed Nadal to break once again in the next game.
Nadal squandered two match points at 4-5 as Fish served to stay alive and ultimately a tie-break was required to settle matters.
A clearly fatigued Nadal - who later revealed he was troubled by a stomach upset - showed his trademark fighting spirit and always held the upper hand in the breaker after an early mini-break.
Having brought up three more match points he then accepted the first as Fish dumped an overhead backhand into the net.