Who is the new Roger Federer?

MELBOURNE, Australia -- Somewhere between the greatest of all time and all washed up stood the newest version of Roger Federer on Wednesday night. Perhaps short of vintage Fed but light years, he admitted, from where he was four months ago, a healthy, newly confident and yes, maybe even vindicated, Federer advanced to his 11th straight Australian Open semifinal with a relatively easy victory over Andy Murray.

In a comeback of sorts for both players: Murray had back surgery four months ago following a great 2013, and Federer has back problems and is coming off a career decline. So in some respects, this one qualified as a victory for both players.

But though Murray proved his body could hold up to the highest level of tennis for 3½ hours, Federer, with his 6-3, 6-4, 6-7 (6), 6-3 victory, moves on to play the waiting Rafael Nadal while generating still more fuel to the never-ending and always entertaining debate about his future.

A new racket with a bigger face. A new coach with a serve-and-volley philosophy. A faster playing surface at the Australian Open. It always has to be something, it seems, with Federer. And indeed, the more powerful weapon in his right hand and new voice in his head in Stefan Edberg have combined these past two weeks to produce a player who certainly looks more aggressive and better equipped to challenge for more Grand Slam titles.

But, as the 32-year-old pointed out with a smile, "The racket's not going to do the running for you," he said. "What I used to do so well, the transition game from defense to offense, I definitely sensed that today, I am back physically. I'm explosive out there. I can get to balls. I'm not afraid to go for balls.

"Last year at times [I] couldn't do it, but [what's] important is that I can do it now."

Asked how Federer's play compared to five years ago when their rivalry began, Murray said it was difficult to answer, that the margins are "very, very small" at this level.

They did not appear, however, so small early Wednesday night, as Federer jumped to a 2-0 lead in sets and was serving for the match at 5-4 in the third. It looked like it would be quick work for Federer until Murray created his first break opportunity in 15 service games and capitalized on his second break try to knot the set at 5-all.

Federer had another opportunity in the tiebreaker with two set points at 6-4, but a newly fired-up Murray, who was more outplayed than playing badly at that point, forced Federer into consecutive forehand errors, then capitalized on his first set-point opportunity when Federer pushed another forehand long.

If there was a momentum change, it lingered two games into the fourth set when Federer jumped to a love-40 lead on Murray's serve but failed to capitalize on six break-point chances in an 18-minute, 56-second, 27-point game.

Federer admitted he became passive and more reluctant to come to the net from the late stages of the third set and into the fourth. But sensing, he said, that Murray was wearing down physically, he seized the chance to break in the eighth game for a 5-3 lead, then served out the match with an ace.

Murray, as is his way, was cautiously optimistic afterward.

"I don't know how many players have come back from surgery and won the first Grand Slam back in their second tournament," he said. "[It's] very unlikely to happen. I just need to use this as, I guess, a steppingstone to getting better and be happy that I've got through five matches. The last two were particularly tough.

"Yeah, I'm playing at a decent level fairly quickly again. Hopefully I'll be back playing my best tennis soon."

Federer, meanwhile, while falling somewhat short of shouting from the rooftops, reveled in rediscovering the simple gifts that were always at his disposal.

"Physically, I know that I can do it," he said. "And then because I'm feeling good physically, then I can really think about tactics I want to play, how aggressive or how passive do you want to play. I have all these opportunities now."

Against Nadal, who owns a 22-10 advantage in their head-to-head series (including 7-2 on outdoor hard courts and 8-2 in Grand Slams), Federer faces a player who dropped his first set in the tournament in the quarterfinals, but as has always been his trademark, did what he had to do to win.

Now two matches shy of becoming the only man in the Open era to win each of the four Grand Slams at least two times each, the tournament's top seed simply outworked his 22-year-old opponent, Grigor Dimitrov, 3-6, 7-6 (3), 7-6 (7), 6-2.

But Nadal, who has been suffering with a painfully raw blister on his racket hand that has affected his serve the most, said he relied on other strengths Wednesday.

"I am sure that you need to be strong physically," he said. "But at one point it's more mental than physical. The emotion to keep playing, the motivation to win the match, makes you resist little bit more and little bit more, and you always want a little bit more.

"That's what I am thinking when I am tired: I can do it. I can [do it a] little bit more. [This] happened in the past, happened a lot in the past that I resist [in] tough matches, so that gave me the confidence that I can do it again."

After falling out of the top five last year and failing to reach a Grand Slam final for the first time since 2002, it is a mantra Federer hears as well.

"The whole retirement question started like in '09," he said. "Here we are five years down the road and I'm getting asked less. So that's a good thing. [But] then I think it's OK to talk about age because, yeah, I'm not 22. But most of the guys now are between 26 and 28 now and have a lot of miles on their body, so I'm not the only guy.

"Yeah, things don't get easier. But at the same time they might become more enjoyable. Maybe I can play with less pressure. Maybe I just love it. I still love competition. I still feel maybe there's something big around the corner. I'm just trying to find out and see if that's the case. I do feel it is. But only time will tell if it's possible or not."