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Rafael Nadal suffers only his seventh loss (51-7) of the 2019 season on Monday at the Nitto ATP Finals.

Nadal: 'I Was Not Good Enough'

Spaniard falls to 0-1 in Group Andre Agassi

Rafael Nadal found one big positive to take away from his surprise 6-2, 6-4 defeat to Alexander Zverev on Monday night at the Nitto ATP Finals: The Spaniard is pain-free.

The World No. 1 pulled out of his Rolex Paris Masters semi-final on 2 November after feeling a strain in his abdominal while serving in the warm-up. But Nadal said he didn't feel any such pain during his first match at The O2 since 2017.

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No complaint about the physical condition. No pain in abdominal. That's the only positive thing, honestly. That's all. Happy the way that [the] abdominal [felt], and hopefully I can continue like this, because it's true that I was not able to create a lot of practice and a lot of effort on that part of the body since last Saturday,” Nadal said.

The physical issue was not an excuse at all. The only excuse is I was not good enough tonight.”

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Nadal fell to 5-1 against Zverev in their FedEx ATP Head2Head series and was unable to get much going against the offencive-minded German, who is trying to become the first player to win back-to-back Nitto ATP Finals titles since Novak Djokovic in 2014-15.

Zverev, with 28 winners, more than doubled Nadal's total (13).

I stay positive. I stay competitive, something that today I was not,” Nadal said. “That's the thing that I am more disappointed [with], because knowing that I will not be at my 100 per cent in terms of feelings, in terms of movement, in terms of confidence or hitting the ball, I needed my best competitive spirit this afternoon, and I was not there in that way.”

Nadal is looking to finish year-end No. 1 for the fifth time and draw even with Novak Djokovic and Roger Federer. The top seed currently leads Novak Djokovic by 440 points in the battle for year-end No. 1.