Andy Murray's state of mind is notoriously tough to judge but as he bids to reach the quarter-finals of the Australian Open here today, there is an undoubted sense of contentment in the Scot's camp that bodes well for the next week.

He is not running around the grounds at Melbourne Park with a grin on his face but the two-time Grand Slam champion is enjoying life, enjoying tennis and looks ready to compete for another major title.

At about 9.30am UK time today, Murray will take on Grigor Dimitrov, the Bulgarian who ended his title defence at Wimbledon last summer, one of Murray's most disappointing losses of the year.

That match, Murray says, was just an off-day, the kind experienced by Roger Federer here on Friday as he was beaten by Italy's Andreas Seppi, although he did admit that maybe he was not quite feeling 100%.

"I felt slow on the court, I felt sluggish and I made mistakes I don't normally make," Britain's No 1 said. "When I tried to make more balls rather than just going for a shot - because I was making a lot of errors at the beginning of the match - I still felt like I was making mistakes.

"I did a few physical tests after Wimbledon last year that maybe suggested there were a few things that weren't quite where I wanted them to be but I was just hitting the ball very badly that day and I don't know why exactly."

This time, Murray is confident things will be different and Britain's Davis Cup captain and the man who coached him when he was a teenager, Leon Smith, believes he is in the perfect frame of mind to succeed here.

"I haven't seen him this happy in a long time," Smith told the Sunday Herald. "Around the practice sessions it's obvious that he's made the right call with the coaching set-up. He's open, he's good fun, he's relaxed, he's practising well and there isn't any tension around. I think he's in a really good place."

The decision to end his association with his assistant coach, Dani Vallverdu, and fitness trainer Jez Green last November raised a few eyebrows.

Rumours they were upset with the way in which Murray brought in Amelie Mauresmo were rejected by Vallverdu last week and the trio remain on good terms, as Murray does with all of his former coaches.

Anyone who has seen Murray and Mauresmo in training here, and since the start of the year, can see they are enjoying their time together and that enjoyment is transferring itself to the court.

Straight-sets wins over Yuki Bhambri of India, Australia's Marinko Matosevic and in round three, Joao Sousa, were to be expected but also notable for their efficiency.

This is the seventh time - and the third in a row - that Murray has reached the fourth round here without dropping a set, a remarkable record but testament to the work he puts in during the off-season.

That is all the more impressive given the reputation the Australian Open has for upsets but having reached the final three times, and reached one semi-final and the quarter-finals last year, he clearly feels at home.

Much has been made about the step up in class Murray will face when he plays Dimitrov but the Scot will also have to adjust to playing inside the Rod Laver Arena and in evening conditions for the first time here this year.

But there will be no room for excuses and Murray will know better than anyone that with Federer gone, and with huge doubts over Rafa Nadal's ability to stay the course, this could be another golden opportunity to get to another Grand Slam final, even if he will not let it affect him.

"I think this is maybe the 10th, ninth or 10th year I've played here and I know how to deal with that and to just concentrate on each match," Murray said. "A lot can change in a couple of days in sport. You have just got to concentrate on your own matches, take care of business, and that's it."

That means seeing off Dimitrov, who is closing in on a place in the world's top 10 and who will go in with confidence after that Wimbledon win.

Murray's quarter-final run here last year was a good effort following his back surgery the previous September but he wants more, and his game, clearly, is in good shape.

"Andy is a much better player from this time last year because he's played so much more and he's back to playing well, so well," Smith said. "He's going after his second serve and I think we're going to see him improve even more as we go on."

The only thing Murray is not happy about, it seems, is the failure of Scottish tennis to capitalise on his success.

His brother, Jamie, who was due in be involved in third-round doubles action overnight here, described the situation as "rubbish", bemoaning the shortage of indoor courts.

"[Andy's] done so many amazing things in his career and you go home and nothing's changed really," Jamie said. "It's a shame because there's a lot of great kids that I'm sure could be top tennis players. They want to be the next Andy Murray but it's just not possible for them. Or it's very, very difficult."

Andy, Jamie and Judy Murray discussed the situation when they were together at Christmas and the youngest member of the family believes something has to be done.

"Clearly it's not as accessible [as it should be]," he said. "They haven't built more better facilities. Indoor courts are obviously expensive. One of my suggestions was they build practice walls. You don't need somebody to play with. It's the same level. You can play with a practice wall if there's nobody else.

"There doesn't seem a place for the kids to play. It's a shame. I don't know as much about it as Jamie and my Mum, they have been talking about it for quite a while [but] clearly it's not great."