* Nadal crushes 92nd-ranked Ukrainian
* Spain 2-0 ahead after opening singles
* Nadal also to play doubles on Saturday (Adds Nadal to play doubles, byline)
By Iain Rogers
MADRID, Sept 13 (Reuters) - A ruthless Rafa Nadal made a seamless transition from hard court to clay when he crushed Sergiy Stakhovsky of Ukraine 6-0 6-0 6-4 to give Spain a commanding 2-0 lead in their Davis Cup World Group playoff in Madrid on Friday.
Turning out for his country only four days after his U.S. Open triumph in New York, the world number two showed no sign of fatigue or sympathy for his 92nd-ranked opponent as he dismantled the hapless Stakhovsky in devastating fashion at the futuristic "Magic Box" venue.
Clubbing winners apparently at will on the Manolo Santana showcourt, Nadal put Spain firmly in control following Fernando Verdasco's 3-6 6-4 6-4 6-2 success against Ukrainian number one Alexandr Dolgopolov in the opening singles rubber.
Stakhovsky, who caused a sensation at Wimbledon this year when he beat seven-times champion Roger Federer in the second round, raised his arms and was given a rousing cheer when he won the opening game of the third set.
He found the inspiration to hold serve three more times before Nadal secured the crucial break to lead 5-4 and clinched victory on his first match point when Stakhovsky sent a backhand service return sailing beyond the baseline.
It was the first time in 769 career singles matches that Nadal has won the opening two sets of a best-of-five set encounter 6-0.
"Obviously it's not the ideal thing physically to change surfaces in a couple of days," the Spaniard said in a courtside interview with Spanish television broadcaster Teledeporte.
"But it's always special for me to play on clay and it's a surface that I love," the 27-year-old added.
"I had only a very short time to adapt but I more or less felt fine."
Spain need one more point for victory in the best-of-five tie and could wrap things up in Saturday's doubles as they bid to preserve their place in the elite World Group.
Captain Alex Corretja said Nadal would partner Marc Lopez, while Ukraine's designated doubles pair is Denys Molchanov and Vladyslav Manafov.
There had been doubt over Nadal's participation after his exertions at Flushing Meadows, where he beat top-ranked Novak Djokovic to claim a second U.S. Open title and his 13th grand slam singles crown.
He has not played in the Davis Cup since helping Spain to victory against Argentina in the 2011 final in Seville, their third triumph in four years and fifth overall.
After Friday's stroll against Stakhovsky, the French Open champion has now won 21 of his 22 Davis Cup singles matches, including a perfect 17 out of 17 on clay.
"We don't have it wrapped up yet, there is still one point to get and we have to be careful," Nadal said.
Spain are in the playoffs after losing away to Milos Raonic's Canada in the first round in February when Nadal, who had just returned from an injury layoff, did not feature.
Djokovic picked himself up after his U.S. Open defeat to help Serbia move ahead against Canada in Friday's World Group semi-finals, while holders Czech Republic led Argentina 1-0.
In other World Group playoff matches, world number three Andy Murray beat 16-year-old Croatian Borna Coric 6-3 6-0 6-3 as Britain ended the opening day 1-1 in Umag.
Switzerland were unable to call on Roger Federer but took a 2-0 lead against Ecuador, with U.S. Open semi-finalist Stanislas Wawrinka getting his side off to a winning start.
Germany also opened up a 2-0 lead against Brazil. (Editing by Martyn Herman)