Nadal's poise and shotmaking came to the fore when 13th seed Sock threatened to take a stranglehold on the second set.
“That was the key of the second set, two-love (down), 15-40,” Nadal said in a courtside interview. “With three-zero a player like Jack, you’ll probably be thinking third set.
“It was a double positive thing. I saved that game and got the break back (in the next game). The match was much closer than the result says.”
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Nadal could face his long-time nemesis Federer in the final, with the Swiss, who has a Thursday quarter-final against Tomas Berdych, on the other side of the draw.
Federer and Nadal have met twice this year, with Federer winning both times, in a memorable five-set final at the Australian Open and in a one-sided straight-sets fourth-round thumping at Indian Wells two weeks ago.
But Nadal is not looking ahead to Federer, because his semi-final opponent Fognini presents a potential banana skin. Nadal has a 7-3 career record but is mindful he lost to the Italian in a five-set thriller on the U.S. Open hardcourt in 2015.
"It’s like a dream maybe,” said the 29-year-old Fognini after becoming the first unseeded player in 10 years to make the Miami semis.
“This is a big, big tournament for me. I’m happy about my performance. I’m just trying to be focussed on my game and do my best.”
(Reporting by Andrew Both in Cary, North Carolina; Editing by Greg Stutchbury/Peter Rutherford)
