Rafael Nadal admits a savage blister on his racquet hand is undermining his Australian Open campaign at Melbourne Park.

The world No.1 was treated twice for the injury during a typically tenacious 3-6 7-6 (7-3) 7-6 (9-7) 6-2 quarter-final triumph on Wednesday over Bulgarian dangerman Grigor Dimitrov.

Nadal coughed up seven double-faults and conceded the deep wound was causing him big concerns ahead of a semi-final blockbuster on Friday night with four-time winner Roger Federer or Wimbledon champion Andy Murray.

The Spanish braveheart twice had his left hand extensively re-taped during his intense three-hour, 37-minute struggle and said trying to serve with the injury was becoming a major worry.

“I feel that with the tape, I can lose the racquet when I’m serving,” he said.

“That’s my feeling. The racquet can go. That’s a terrible feeling for a serve, because then when you have this feeling, you are not able to accelerate at the right moment.

“You lose a little bit the coordination. That’s a big deal.”

Nadal said his serving troubles were also affecting the rest of his game.

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

“So I’m going to try to improve that for after tomorrow that I need.

“If not, I not going to have the chance to be in the final.”

His injury aside, Nadal also had to overcome a one-set deficit against Dimitrov and multiple set points in the pivotal third to advance to the last four for the fourth time.

“I was so lucky,” he said.

“I felt like anything could happen in the third set. I hurt a lot … I’m very, very happy.”

Dubbed “Baby Fed” for a silky playing style uncannily similar to Federer, Dimitrov showcased all his talents – including an audacious under-the-legs lob – to push Nadal to the limit.

The signs were there early that Nadal might be in for a long afternoon when a couple of uncharacteristic shanks handed Dimitrov a break in the second game of the match.

It was the only opening the underdog needed as he clinched the first set with a thundering ace.

Upping the ante, Nadal whipped a signature off-forehand winner to break Dimitrov for the first time to creep ahead 2-0 lead in the second set.

But the top seed gifted the break right back with three double-faults before hitting back in the second-set tiebreaker, ripping a forehand down the line to create three set points.

He only needed one, the Spaniard celebrating like he’d won the title after sending a ridiculous backhand flick past the 22nd seed to square the match up.

Clearly bothered by the nasty big blister, Nadal called for the trainer for the first time midway through the third set and moments later dropped serve again with a sixth double-fault.

He conjured up three big serves to hold from set point down to force a second tiebreaker, which he snatched after Dimitrov blew two more set points with rueful forehand blunders.

Two scorching backhand passes earned the top seed the decisive break early in the fourth set and, when he grabbed another in the eighth game, the 2009 champion was through.