London - Rafael Nadal battled to his third successive win at the ATP Tour Finals, but his marathon 6-7 (2/7), 6-3, 6-4 victory over David Ferrer might prove a significant blow to his chances of defeating Novak Djokovic in the semi-finals.
Despite having already booked his place in the last four, Nadal refused to conserve his energy in a meaningless match against his fellow Spaniard that came just 24 hours before his clash with world number one Djokovic.
While defending champion Djokovic rested after completing his group campaign on Thursday, Nadal slugged it out with Ferrer in a draining baseline battle that lasted two hours and 37 minutes.
The sight of Nadal pushing himself to the limits against Ferrer will have made for enjoyable viewing for Djokovic, who had promised to watch the match to get a glimpse of his semi-final opponent's form.
It will take a remarkably quick recovery from Nadal if he is to end Djokovic's bid for a record fourth successive title at the prestigious season-ending event at London's O2 Arena.
Nadal certainly has plenty of motivation to drag one last effort from his aching limbs as he attempts to end the worst year of his career on a high.
Andre Agassi is the only man ever to have won all four Grand Slam titles, a Olympic singles gold medal, the Davis Cup and the Tour Finals, but he would have Nadal for company if the 29-year-old lifts the trophy on Sunday.
Nadal had routed French Open champion Stan Wawrinka and world number two Andy Murray in his first two Tour Finals matches -- the first time he had beaten two top four opponents in the same tournament since 2013 -- while Ferrer had already been eliminated after losing his first two matches.
Ferrer's dismal career record of 23 defeats from 29 meetings with Nadal suggested more misery was in store for the 33-year-old when the former world number one raced into a 3-0 lead before most of the crowd had even settled into their seats.
As quickly as he seized the initiative, Nadal let it slip from his grasp as Ferrer broke twice to win four games in a row.
Nadal still had a chance to serve for the set after breaking for a 6-5 lead, but he couldn't finish the job and Ferrer eventually won it in a tie-break.
Nadal's response to dropping a set for the first time in this year's tournament was to breeze through the second to level the match.
Unable to convert five break points in a 14-minute marathon first game of the final set, Nadal found himself dragged into another prolonged struggle with the tenacious Ferrer.
But there was still no sign of Nadal saving his body for the Djokovic match and his perseverance was rewarded when he broke at 4-4 to set up the win.