GARBINE Muguruza is through to what is surely her first of many Grand Slam finals after beating Agnieszka Radwanska in three sets.

The No 20 seed, who had never previously been further than the quarter-finals in any major, won 6-2, 3-6, 6-3, withstanding a fightback from her Polish opponent and a slight attack of the nerves when victory was in sight.

The big question when the 21-year-old Spaniard faces Serena Williams in Saturday's final is whether those nerves return. If they do, the American should easily complete the full set of majors, being the holder of the US, Australian and French Open titles already. If they do not, Muguruza has the physical power and the athleticism to put in a real challenge.

The No 20 seed showed her quality from the opening games of her match against Radwanska, twice breaking the former finalist's serve on her way to taking the first set. But she showed her nerves in the second, contriving to lose it despite being 3-1 and 30-15 up on her opponent's serve.

When Muguruza was broken in the first game of the third set it looked as if Radwanska's superior experience would tell, but the younger woman hit back immediately, then broke again for 4-2. Both players looked shaky as the end neared, and there was a remarkable moment in the last game when Radwanska challenged a shot apparently after hearing a voice from her box shout "Out". She was wrong, and as a result found herself match point down. Three strokes later she found herself out of the tournament.

Muguruza admitted that, with the match in her hands, she had begun to panic, and only recovered her form once she had to fight to get back top. "I was like, okay, wait - you're the only one that can lose this match," she said of her second-set slump.

"I just get really nervous. And I think Radwanska was waiting for this moment. She fought, she won the second set.

"But I was: 'Okay, be calm. You're playing against Agnieszka. It's going to be a tough match'. In the third, I could find a way, as in the first set, [to] play more aggressive, lose the fear to win the match."

Muguruza has beaten Williams once in their three meetings to date - in the second round at last year's French Open - so she knows it can be done. But that fear needs to stay lost if she is to derail the American's hopes of a sixth title.