Rafael Nadal warned he needed to quickly improve his misfiring serve  hampered by a large blister on his left hand  or face defeat in the Australian Open semi-finals. Photo by: David Gray

Melbourne – Rafael Nadal Wednesday warned he needed to quickly improve his misfiring serve – hampered by a large blister on his left hand – or face defeat in the Australian Open semi-finals.

Nadal got home 3-6, 7-6 (7/3), 7-6 (9/7), 6-2 against Grigor Dimitrov in the last eight and will now play either Andy Murray or Roger Federer for a place in Sunday's final.

But the world number one's serve, compromised by an ugly-looking blister in the palm of his left hand, was vulnerable and he gave up seven double-faults, including two of them on break points.

The inconvenience threatens to derail Nadal's hopes of a second Australian title following his triumph in 2009 and his 14th Grand Slam crown overall.

“I felt that the biggest problem was the serve because, you know, serving like this gives me a problem for everything else,” he said.

“When you lose the confidence with one shot, one important shot, then you are not able to play the rest of the shots calmly.

“So I'm going to try to improve that, because I'll need it the day after tomorrow. If not, I'm not going to have the chance to be in the final.”

Nadal said protective tape over the blister meant he could play on, but badly affected his serve because of the loss of feel.

“With the forehand it's not a big issue (but) with the serve, a little bit,” Nadal said.

“I feel that with the (protective) tape I can lose the racquet when I'm serving. It's a terrible feeling for a serve, because when you have this feeling you are not able to accelerate at the right moment.

“I lost a little bit of coordination. Yeah, that's a big deal. I served slower. I served bad.”

Nadal was playing after three-time defending champion Novak Djokovic was upset by Stanislas Wawrinka late on Tuesday, and there were times when he looked like becoming another casualty.

For long passages of the quarter-final on Rod Laver Arena, Nadal was struggling to put away the 22nd-seeded Dimitrov, and he needed a bit of luck at crucial stages to go through.

The statistics showed how Nadal struggled with 47 unforced errors outnumbering his 42 winners and his serve was broken three times.

“I was so lucky, after saving set points in the third set,” he said. “He just missed an easy forehand... Today was for me, so I'm so happy.”

Dimitrov, 22, who was bidding to become only the second Bulgarian to reach a Grand Slam semifinal, showed what an emerging talent he is to have Nadal under pressure for long periods.

Nadal's opening serve was broken and Dimitrov controlled the remainder of the set as the 13-time Grand Slam champion dropped his first set of the tournament.

Nadal began to test the legs of the young Bulgarian with some longer, physical rallies in the second set, but after breaking Dimitrov's serve he handed back the break with three double-faults in the third game.

The set went to a tiebreaker which Nadal comfortably won with an exquisite backhand flick across court to level the match.

But just when the top seed looked to be getting on top, after breaking the Bulgarian's serve in the fifth game, Nadal's shaky serve again cost him with a double-fault on break point.

Nadal fought off set point as the third set went into another tiebreaker and he was fortunate to survive after Dimitrov just missed a forehand winner to the corner on his first of two set points.

Nadal quickly seized the advantage to get to set point, and Dimitrov lost the set with an overhit forehand off a net cord.

Dimitrov was broken in the second game of the final set, after six deuces, on a Nadal backhand pass and the Spaniard went on to claim victory on his fourth match point. – Sapa-AFP