Istanbul - Even after 15 Grand Slam titles and at the age of 31, Serena Williams says the best is still to come, after ending a remarkable comeback season with the WTA Championships title she first won over a decade ago.
"I definitely think I can improve some more," she said after battering an in-form Maria Sharapova to a 6-4, 6-3 defeat with an outstanding display of serving and heavy hitting in Istanbul on Sunday.
"Especially when I was out there I thought, 'Okay, I want to work on this in November' (during the close season). And, 'Oh, okay, I'm going to work on that one in November'.
"So, I was thinking of all these things I can work on and I can improve on. I think every day, whether it's life or whether it's playing tennis, we always can improve as people or as whatever we do.
"The day I feel that I can't improve, I think that's the day I should probably hang up my racket."
If Williams' prediction is right, then the achievements of Martina Navratilova and Chris Evert, who each won 18 Grand Slam titles, may be within her reach. That has only been bettered during the open era by Steffi Graf, who won 22.
Williams has won the Olympics, Wimbledon and US Open titles in the last four months - a dramatic turn-around from a 12-month absence in 2010 and 2011 in which she suffered from a badly cut foot and life-threatening blood clots on her lungs.
The US player is probably capable of improving her net game in singles significantly and perhaps varying the pace and angles of her ground strokes more as well. The crucial imponderable will be her ability to maintain fitness.
Though she is only world ranked three, behind Sharapova and the year-end world number one Victoria Azarenka, the American is likely to become the bookies' favourite to win the next Grand Slam, the Australian Open in January.
Williams was reluctant to agree with the suggestions but said another "Serena Slam" - holding all four Grand Slam titles simultaneously - was possible: she would have to win both the Australian and the French Open title in June to achieve that.
"I don't know. I could. We'll see. I have a chance. Hopefully," she said, mulling over the idea.
It would be unwise, though, to overlook the prospects of Sharapova, despite the Russian having lost nine times in a row against Williams since beating her in the 2004 Wimbledon final.
Sharapova has gradually remodelled her game well after suffering the kind of rotator cuff shoulder injury from which most players never fully recover.
"I'm proud that I'm moving in the right direction in improving my game. I've accomplished a lot of things this year I really wanted," she added, referring partly to the French Open title which completed her career Grand Slam.
"I have a lot of positive thoughts moving into next year."