MELBOURNE (Reuters) - A key to becoming a grand slam champion is managing the off-days that are almost inevitable in a two-week tournament -- a skill Grigor Dimitrov showed to good effect on Friday.

Tennis - Australian Open - Rod Laver Arena, Melbourne, Australia, January 19, 2018. Grigor Dimitrov of Bulgaria celebrates winning against Andrey Rublev of Russia. REUTERS/Thomas Peter

The 26-year-old was not at his best against feisty young Russian Andrey Rublev, winning the Australian Open third round tussle 6-3 4-6 6-4 6-4 despite racking up 61 unforced errors.

“When you don’t feel well during the match, you need to find other courses to take,” world number three Dimitrov, told reporters. “The mental game, especially on days like today, comes more in play than the game itself.”

Dimitrov has been lauded as a potential winner of the game’s biggest prizes since becoming Wimbledon junior champion in 2008 with an easy style likened to that of the great Roger Federer.

When he beat defending champion and home hero Andy Murray to reach the Wimbledon semi-finals in 2014 and crack the world’s top 10 it seemed that greatness beckoned.

That proved a false dawn, however, and it was not until last year’s Australian Open that the Bulgarian reached his second grand slam semi-final, losing a five-setter to Rafa Nadal.

The intervening period saw Dimitrov slide to 40 in the rankings and go two and a half years without a title.

For all the days when he looked like a world beater, there were still defeats by the likes of Mikhail Kukushkin, Viktor Troicki and Steve Johnson -- fine players but the kind of opposition Dimitrov expects to knock over.

There was a defeat to Rublev, too, at last year’s U.S. Open. But there were also four titles, including becoming the first debutant champion since 1998 at the ATP Finals in November.

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For a while in the second round here it looked as though the old vulnerability had returned as he flirted with danger against American qualifier Mackenzie McDonald, losing the fourth set 6-0 before squeezing through in five sets.

Against 20-year-old Rublev he was a set and break to the good before the serve misfired and errors crept in to find himself at one set apiece and a break down in the third.

Trailing 4-2 the alarm bells were sounding, but Dimitrov turned things around to regain control.

He broke a hot-and-bothered Rublev in the seventh game of the fourth set and, despite a slight stutter when serving for victory, he chased down a Rublev volley to ram home a forehand winner. His victory celebration spoke volumes.

Dimitrov said that having so many tools in his locker helps him, as does knowing which one to use. However, his opponent in the next round, Nick Kyrgios, arguably has more.

“I was not finding the angles that I wanted, but when that fails you kind of go on to the next one,” Dimitrov said.

“My serve, for example, failed me, too. What are the other options? The one thing I’m very happy with is I feel I have a big arsenal of tools to kind of deal with any circumstances.

“How I win right now, I love it. On days that you don’t feel the best, these are the matches that count a lot.”

Greater challenges await here, but Dimitrov has proved the old adage that you cannot win a grand slam in the first week, only lose it.

“The bigger upside is it can only get better from now,” he said. “Hopefully the next match.”