By Joshua Schneyer
RIO DE JANEIRO (Reuters) - Defending Olympic champion Andy Murray reached the semi-finals of the men's tennis on Friday after winning a third-set tiebreak to scrape through a testing encounter against American Steve Johnson.
Britain's Murray, the world number two, edged into the last four with a 6-0 4-6 7-6(2) victory but was pushed to the limit by the 22nd-ranked Johnson, who came back to win the second set after being brushed aside in the first.
The players traded service breaks and blazing passing shots in the final set but Murray showed steady nerves to win the tiebreak, closing out the hard court match with a deftly placed overhead smash.
Murray will face the winner of a match later on Friday between Japan's Kei Nishikori and Gael Monfils of France.
In the first women's semi-final of the Games, Puerto Rico's Monica Puig beat Petra Kvitova of the Czech Republic for a spot in the gold-medal match.
Puig, ranked 34 in the world, won a decisive third set to go through 6-4 1-6 6-3. She will compete in the final for what may be her country's first medal of the Games, and its first ever gold.
"It would be unbelievable and it would be the biggest honor in the world," Puig told reporters about the prospect of winning gold. "The island is full of such bad news all the time, so every time there's a Games and somebody from the island wins a medal everything stops and I know how happy people get."
Island nation Puerto Rico, which has been facing a deep financial crisis, has captured a total of just eight medals at past Games, mostly in boxing.
Puig will take on either American Madison Keys or Angelique Kerber of Germany in the final.
On the other side of the men's draw, Rafa Nadal of Spain was playing home favorite Thomaz Bellucci of Brazil on Friday. Belucci captured the first set 6-2 but Nadal fought back to win the second 6-4, forcing a third and final set in a center court stadium brimming with rowdy Brazilian fans.
The winner will take on either Argentina's Juan Martin del Potro or Spain's Roberto Bautista Agut in the semi-finals.
The Olympic tennis tournament has been marked by upsets with both the men's and women's top seeds, Serbia's Novak Djokovic and American Serena Williams, knocked out in the early rounds.