Mixing the top eight players in London for the ATP's grand finale should be a recipe for thrilling fare but a large crowd were again left short-changed on Monday with Swiss Stanislas Wawrinka the biggest disappointment.

Wawrinka, who produced arguably the year's standout performance when he beat Novak Djokovic in the French Open final, appeared at times to be going through the motions against Rafael Nadal in the night session at the ATP World Tour Finals.

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Rushing through points and spraying 35 unforced errors, world number four Wawrinka, who lost an epic semifinal here last year to Roger Federer, collapsed to a 6-3, 6-2 defeat.

In the day's earlier Ilie Nastase Group match, home favourite and world number two Andy Murray was at least made to scrap for his 6-4 6-4 win over dogged Spaniard David Ferrer.

With Djokovic hammering Japan's Kei Nishikori on Sunday and Federer cruising past Tomas Berdych it means 14 of the last 16 group matches at the prestigious and much-hyped season finale, have been won in straight sets.

"I don't know. Was just a really bad day at the office. Many little things that weren't good today," 30-year-old Wawrinka, who is guaranteed $167,000 just for showing up, told reporters when asked about his performance.

"It's a really bad match. Bad behaviour in the second set. Things weren't too great about myself.

"Just disappointed in general. Everything went wrong. Just everything went the wrong way. Simple."

While Wawrinka was poor, it was another positive step for Nadal as he tries to rediscover the kind of form that delivered 14 grand slam titles and the world number one ranking.

Things did not start well when he lost his opening service game to love, but he replied immediately in similar fashion and moved 5-3 ahead when his opponent blazed a forehand wide.

He failed to convert any of the seven break points a rattled Wawrinka offered up at the start of the second set and then saved two himself in the next game, one with a stunning lob.

Wawrinka then crumbled.

"Every day for me now is an opportunity to enjoy on court, enjoy the competition, something that I missed for moments this year," Nadal, who fell to 10th in the rankings during a miserable summer, said.

With Murray up next on Wednesday, however, Nadal played down expectations that he could yet end a below-par year with his first ATP Tour Finals title, having twice been runner-up.

"I won the first match, that's all. I cannot think about that, seriously."

Murray, despite having one eye on next week's Davis Cup final in Belgium, definitely looks capable of claiming the title and complete the hat-trick of Wimbledon, Olympic gold and Tour Finals in his home city.

The 28-year-old's preparations have been geared towards a claycourt in Ghent rather than the indoor surface at the O2 Arena, but he still toyed with Ferrer at times.

Murray, who already boasted a career-best 68 wins this season coming into the tournament, saved a break point in the opening game and then settled into his groove.

He could not capitalise on three break points in the eighth game but was gifted the opening set with a Ferrer double fault -- one of eight the Spaniard produced.

One lapse, when he was broken to love in the first game of the second set, was quickly corrected as he broke back twice to beat Ferrer for the 12th time in 18 meetings.

Should he beat Nadal on Wednesday Murray will be guaranteed to finish the year as world number two.

"It would be obviously nice to finish number two because I haven't done it before, but it's not a goal that I'd set for myself at the beginning of this year," Murray said.

More important will be helping Britain win the Davis Cup for the first time since 1936.