Four-time Barclays ATP World Tour Finals champion Roger Federer survived a scare on Sunday evening against Spain’s Fernando Verdasco before prevailing 4-6, 7-5, 6-1 in the second Group A match at The O2 arena in London.

“It was a crucial match for me to get off with a win in the round-robin stages,” said Federer. “Fernando is a great player and I’m happy I was able to come through.”

Victory in his first round-robin match sees Federer inch closer to reclaiming the title of ATP World Tour Champion. The Swiss finished atop the South African Airways ATP Rankings for four years between 2004-07 before being dethroned by rival Rafael Nadal last season.

The two are once more locked in a battle for the year-end No. 1 ranking and, by winning his opening match, Federer added 200 points to his total and increased his lead over the Spaniard to 1,145 points. Nadal opens his campaign on Monday afternoon against Sweden’s Robin Soderling.

Playing at the season finale for the eighth straight year, it was a below-par Federer who took to the court. Coupled with coming up against an inspired Verdasco, determined to record his first win in four meetings with the Swiss, Federer made life hard for himself with an uncharacteristically high unforced error count in the first set.

After being on the receiving end of two lethal forehands in the opening game, which he lost to love after a double fault on the first point, Federer focussed his attentions on attempting to wear down the Verdasco backhand. The Spaniard was equal to the task though and grew in confidence as the set wore on, clinching it 6-4 with a rifling backhand pass that shook Federer’s racquet.

Federer was still not at his best in the second set, but showed his battling qualities as he produced a far-improved serving display to keep ahead. With the set approaching the crunch stage, Federer stepped up to the plate and attacked Verdasco and reaped the rewards. A nervous Verdasco failed to find the required zip on his serves in the 12th game and Federer took full advantage with aggressive returns forcing errors from the Spaniard as he levelled the match.

In direct contrast to the first set, it was Federer’s forehands that were drawing gasps from the crowd and Verdasco who was showing signs of frustration at a growing error count in the deciding set. As Federer moved through the gears, he raced through the games and quickly established a 5-0 lead before closing out a hard-fought victory after one hour and 59 minutes.

“I was down a set and only in the second set was I able to sort of get the ball into play, find my range, find my rhythm,” confessed Federer. “I think this is also when I started to feel like I had chances. My first break points, I think I could have had them earlier if I played a bit earlier, but they came for set points, and it was a crucial moment for me because I knew the longer the match went on, the more my belief was going up and his was going down. Then in the third, I was able to play more freely. This is when I was really in the match.”

Federer became the fourth player this season to win at least 60 matches, joining match-wins leader Novak Djokovic (76), Andy Murray (65) and Nadal (64). In a record-breaking season for the Basel native, he has reached the final at all four majors in 2009 – completing the career Grand Slam at Roland Garros (d. Soderling) and winning a record 15th Grand Slam singles title at Wimbledon (d. Roddick). He was defeated in five sets by Nadal and Juan Martin del Potro in the Australian Open and US Open finals, respectively.

The 28-year-old Federer has a staggering 28-5 match record at the Barclays ATP World Tour Finals. He reached five successive finals between 2003-07, winning back-to-back titles in 2003-04 and 2006-07 and finishing runner-up to David Nalbandian in a five-set thriller in 2005. He failed to advance past the group stage for the first and only time in Shanghai last year, decisively losing to Murray in his third round-robin match.

It has been a season of firsts for Verdasco, who is making his debut at the season climax. After intensive off-season work with Andre Agassi’s former trainer, Gil Reyes, the left-hander reached his first Grand Slam semi-final (l. to Nadal) at the Australian Open and won an ATP World Tour hard-court title for the first time at Pilot Pen Tennis (d. Querrey) in New Haven. The Madrid native, who celebrated his 26th birthday one week ago, has compiled a 52-23 mark in 2009.