Murray, Nadal both squeak into semi-finals

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. Spaniard Rafa Nadal also secured a spot in the semi-finals with a hard fought victory against home court favourite Thomaz Belucci of Brazil, rallying back after losing the first set. Britain's Murray, the world number two, edged into the last four with a 6