Roger Federer admits he wished he made it a closer battle for number one spot in the ATP Men's Tennis Rankings between him and Rafael Nadal during the latter half of this season.
The pair have enjoyed successful seasons, winning two Grand Slams each - Federer at Wimbledon and in Australia, and Nadal emerging victorious at the US and French Open.
The duo have 35 Grand Slams between them during their two remarkable careers.
This year, however, the pair came back into the one and two spots after injury-laden seasons for Andy Murray and Novak Djokovic, the latter of which has ruled himself out of action until the 2018 US Open.
The Swiss takes the lion share of those Grand Slams with 19 in total, but Nadal is breathing down his neck and will finish the year at the summit if he wins at the Paris Masters.
It's been a meteoric rise for Nadal and Federer, who were in the shadow of Djokovic and Murray for the duration of 2017 after they, along with Stan Wawrinka, shared the Grand Slam wins last year.
But, even at the age of 36, Federer is still demanding more of himself and is still competing at the highest level. By no means is he resting on his laurels after his comments about not chasing Nadal far enough this season.
“Ever since Rafa won the US Open, I knew it was going to be very, very difficult,” Federer admitted.
“I wish I could have chased [No. 1] more — my only regret is that I couldn’t have chased it more at Cincinnati and the US Open.
“That was a pity — but Rafa played a full schedule, and he deserves it. I’m OK with that.”
The US Open seems to be the crucial point of this feeling of regret from Federer, the 19-time Grand Slam player lost poorly to Juan Martin del Potro.
Federer could have equalled Pete Sampras' record of finishing on top of the rankings at the end of the year for a sixth time.
Federer pulled out of this week’s Paris Masters following victory in the Swiss Indoors title at the weekend, which all-but ends his chances of becoming world number one.
The Swiss has gone home to Basel to rest after feeling 'drained' from a hectic schedule. Fitness indeed has played a part in Federer's credentials at the end of this year.
The 36-year-old will feature in the ATP World Tour finals in London which take place from November 12 at the O2 Arena.
He is the ATP World leader with seven titles won this year, and therefore goes into the contest as a strong favourite.