Andy Murray insists he retains sufficient "desire and fight" to take on the world's best players following his first win over a top-10 opponent in more than three years.
Murray stepped up his return to competitive tennis with an impressive three-set victory over world No 7 Alexander Zverev in the last 32 of the Western & Southern Open.
It was a hugely encouraging display from the Scot, who has lowered his expectations since battling injury problems, including two major hip surgeries.
Despite struggling in recent practice matches and often appearing frustrated on court, the world No 134 displayed steely determination to defeat German Zverev 6-3 3-6 7-5 in two hours and 31 minutes.
Asked if had been expecting to perform so well at the tournament, Murray told a press conference: "If you watched my practice sets and stuff and the build-up to the tournament, you would have said no.
"I was getting belted by everyone. Couldn't win one! But practice doesn't really matter. It's what obviously you do on the match court.
"Sometimes if you're watching from the stands, you might think I get really down on myself and that I'm very negative, and I think outwardly I definitely am.
"But inside me I have a very, very strong self-belief and know that I can win matches like that. I always believe, even when outwardly it seems like I might be flagging or being negative or whatever."
He added: "I trust my competitive instinct. I think that's a big strength of mine.
"I haven't lost that yet. I think once that goes, that's probably when it's time to, you know, for me to call it a day.
"But I still have that desire and fight to try and win matches and compete and get the most out of myself."
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