He was still feeling the effects of jet lag and had just nursed a sore back through his opening victory here yesterday, but Andy Murray was clear about one thing. He now knows what it takes to win one of the four great prizes in tennis.
In the 22 days since he ended Britain's 76-year wait for a male Grand Slam singles champion, Murray admitted that he had yet to come fully to terms with his achievement, but has had time to consider what made the difference during his glorious summer. Having finished runner-up in his first Wimbledon final, the 25-year-old Scot went on to claim Olympic gold before realising a lifetime's ambition by winning the US Open, ending a run of four successive defeats in Grand Slam finals.
Tennis can be the most demanding of sports physically, but Murray believes that the key to making his final breakthrough was all in his mind. He said that thinking on his feet during matches had made the crucial difference.
Despite his victory over Novak Djokovic in last month's final at Flushing Meadows, Murray did not believe that he played his best tennis in New York. At difficult times, however, the Scot stayed focused on his task and worked out a way to win, which he admitted he had not always done in the past.
"I thought I played really well at the Olympics," Murray told me yesterday in the interview room after beating Ivo Karlovic in the first round of the Rakuten Japan Open, his first appearance on court since his historic victory.
"At the US Open I didn't feel like I played that well. Obviously the conditions didn't help. But I played smart tennis. It wasn't always easy to serve well or to hit the ball cleanly from the back of the court, but I found a way to win the matches, even when I wasn't playing well. And that's something that was so important."
Although Murray was hugely impressive in the latter stages of the US Open, beating Tomas Berdych with a masterful display in a windswept semi-final and stopping Djokovic in his tracks after the Serb had levelled the final from two sets down, there were two matches earlier in the tournament when he laboured for lengthy periods. He struggled to break Feliciano Lopez's serve in a third-round match played over nearly four hours in gruelling heat and humidity and was a set and 5-1 down against Marin Cilic in the quarter-finals.
"Sometimes in the past when I've been playing well I would win a lot of matches and then when I wasn't playing well I would get down on myself and not figure out exactly how to win all of the time, especially in the Slams," Murray said. "I think I did a very good job of that at the US Open because I didn't feel like I played unbelievable tennis all the time, although the conditions didn't help. I played smart the whole time and was able to stay focused.
"I was using the time I had at the change of ends and the time between points better. I'd obviously managed to turn the match around against Cilic. That could easily have gone the other way. That was a big turning point."
It was a turning point in the tournament and an even bigger turning point in his career. As he looked back on his summer and ahead to the future, the Scot spoke with an assurance and a self-belief that have perhaps on occasions been lacking in the past. Murray today has the air of a man at ease with himself and with the challenges that lie ahead of him, without giving the impression that he would ever become complacent. He takes his work too seriously for that to happen.
The focus on his tennis extends to refusing to let himself get side-tracked by physical issues. Murray will probably never wear the permanently stony face that his coach, Ivan Lendl, never let slip on court, but he has learned not to become distracted by the inevitable aches and pains that come with modern-day tennis.
During his victory here yesterday over Ivo Karlovic, Murray took a medical time-out to have treatment on a sore back. At his post-match press conference he made light of the problem – "It's nothing serious at all and it feels absolutely fine now" – but later confided that on most days he feels stiffness in his back. He had to have eight pain-killing injections before this summer's French Open.
"It started early in the year," Murray said. "I didn't really think too much of it, but it gradually got worse and worse and worse. I went to see a specialist and got it checked out and got the injections and felt better after that. I still had a few problems from time to time, but I adjusted my training a bit to cope with it. I started doing more exercises to strengthen the area and take a bit of pressure off the problem part.
"My back is stiff most days, but once you start to get warmed up the more matches I play it almost feels better. It almost loosens it off a little bit and I get used to the movements."
Asked how his back was affected by long flights like the 10-hour journey he had to make here, Murray said: "That's not good – and walking around or standing for a long time it gets really sore. If I just sit on my butt for a week or so and do nothing then when I start again it's really stiff. It felt quite cold out there this evening. There was quite a breeze and that didn't help."
Nowhere was Murray's focus more in evidence than at the end of his victory over Djokovic last month. With the Scot leading 5-2 in the final set and about to serve for victory, his opponent – to jeers from the crowd – sent for the trainer to have his legs massaged. Requesting a medical time-out at a crucial stage in a match is a ploy that many players have used to good effect over the years, but Murray refused to let himself be psyched out when on the brink of his finest moment.
The Scot got up from his chair and went to the back of the court, bouncing up and down and giving out the message that Djokovic was only delaying the inevitable. Murray was so focused on his task that he went to serve from the wrong side of the court when play resumed. Minutes later victory was his.
"I felt really, really comfortable at that moment," Murray recalled. "I don't know the exact reason for it, but I think having put myself in that position a lot of times in my head over the last four or five years of my life and thinking about it, when it did actually come I was prepared for how it was going to feel."
He added: "When the match finished I couldn't believe what had happened. I think I was just so in the zone that I wasn't thinking about everything that was going on on the court, about the time-out, about the crowd making a lot of noise, about the fact that I was serving to win my first Grand Slam. I wasn't really thinking about that at all."
Had he been annoyed by the fact that Djokovic had taken a medical time-out? "Not at all. I felt like I was going to win. When I've been serving for matches I've never ever really had any problems with it. Sometimes when I've been up in sets I've let other guys back in, but when I've been serving for sets and matches I was always OK.
"I had played that moment over and over again in my head and thought what it would be like if I served for it. I would get nervous just thinking about it. I built it up to be such a huge thing that when it came it actually wasn't as bad as I had expected."
If winning a first Grand Slam title has given Murray greater self-belief, he said it had also brought a greater sense of responsibility on the court. "Sometimes during the year in certain matches I think maybe I haven't done myself justice," he said. "I felt a little bit after the US Open that I should reset some goals.
"Because winning a Slam was so important to me I felt sometimes that I was focusing on the next Slam rather than on every tournament and every match. Now I feel I can hopefully concentrate better throughout the year and not take my eye off the ball at any tournaments – and take more responsibility for all my performances."