The opening singles clash at the O2 Arena pitted the top two in Group Lleyton Hewitt against each other, yet what unfolded was a one-sided contest that spanned just 64 minutes.

Nishikori failed to replicate his performance in Monday's upset win over Roger Federer, barely putting his rival under any pressure as he committed 24 unforced errors.

Anderson showed no mercy, avenging a straight-sets loss in their recent meeting at the Paris Masters in style to put himself in pole position to make the last four of this year's season-ending event.

The big-serving South African threatened to record a double-bagel result, though his opponent at least dodged that embarrassment by holding serve in the penultimate game of the second set.

Still, Nishikori was a shadow of the player who toppled six-time champion Federer less than 48 hours earlier in the English capital.

It was a surprise to see Anderson need three set-point opportunities to clinch the opener, albeit he sealed it in style with a forehand return on the stretch that clipped the top of the net.

Nishikori left the court after falling behind but the break failed to see a change in fortunes for the Japanese, who continued to make a slew of careless mistakes.

He at least avoided suffering the heaviest defeat of his career - this result matches a loss at the hands of Robin Soderling in Stockholm a decade ago - drawing ironic cheers from the crowd when a clever sliced backhand sealed the sixth game of the second set.

However, it was only a case of delaying the inevitable, a weak backhand return following a booming first serve from Anderson in the next game putting the world number nine out of his misery.