Stan Wawrinka was simply too good for Novak Djokovic in the US Open final, says Mark Petchey

After Stan Wawrinka's superb win over Novak Djokovic in the US Open final, we asked Sky Sports expert Mark Petchey to answer five key questions about the tournament.

The Swiss world No 3 claimed the third Grand Slam title of his career following a 6-7 6-4 7-5 6-3 victory over Djokovic at Flushing Meadows.

Angelique Kerber had earlier replaced Serena Williams as women's world No 1 after winning her first US Open title and Petchey gives his verdict on a number of talking points from the final Grand Slam of the year.

What is the secret to Wawrinka's 100 per cent success rate in major finals?

His record since 2014 is 11 finals in a row, so as much as you focus on the major finals, it's been every time he's been in a final. 

Stan, at times, probably hasn't been quite as consistent as the others ahead of him in the rankings in general throughout the year, but when he's on his game and confident, he's capable of beating anyone. He's obviously shown that in the three major finals. 

Stan played his best tennis on the big points and certainly that was the case against Kei Nishikori in the semi-finals. He was battle hardened throughout the tournament in terms of playing his best tennis on competitive points.  

Were fitness issues to blame for Djokovic's defeat?

To be honest, it wasn't the fitness issues that lost Novak the match, it was the fact that Stan was very good. I think tactically he was very smart, served a lot of body serves, which looked like they upset Djokovic's rhythm a bit. 

Stan's threat comes from the fact he is capable of hitting the ball down the line equally hard off both sides, which very few players are able to do, so that's a huge asset. 

As good as his attack was, there were a couple of moments where his defence was equally as important. I think Novak will look back at the chances that he's had on break points and be a little bit disappointed that he didn't play better when the pressure was on Stan. 

Can Serena regain No 1 spot - or is this the start of a new era?

Serena is not getting any younger, but she is certainly putting herself in positions to win these tournaments, time and time again. I certainly think that Serena has got another good one or two years left in her, right at the top of the game. By that, I mean being in the top two, top three in the world. 

Whether the motivation is for her to get back to No 1, she may end up having to play a more enhanced schedule to do that. It's obviously something she has not tended to do in the past. She's managed her schedule magnificently, that's why she's still playing as well as she is at this age. 

Over the next few months, she will be thinking about what's going to happen in 2017 and whether the No 1 ranking will be more important to her than winning one, two, three more majors. 

Was the US Open a step too far for Andy Murray?

I think Andy was really unlucky this year. Had it been a normal year, without the Olympics, it would have made life a lot easier for him. We all saw how much he gave in Rio and how much that took out of him. 

He did phenomenally well to make the final in Cincinnati just after it. Had he not been close to world No 1, there is a real chance he would not have even played in Cincinnati. 

In some ways, he's been a victim of the schedule and his own success in the last few months. It was always going to be very tough physically, but he's had an amazing summer and I don't think he needs to change anything right now. 

Will Murray play in Davis Cup semi-final against Argentina?  

Yes I do. Andy showed his commitment to the Davis Cup by flying to Serbia after winning at Wimbledon. In my own mind, there is no doubt that he will play.

He's probably running on fumes at the moment, but will want to go out there and give it his all in the Davis Cup. It's obviously important for the team that he does get out there and play. Whether he feels he can play three days in a row, is something he will talk about with captain Leon Smith closer to when the tie gets underway.