Roger Federers chances of progressing to the knockout stages of the ATP Finals have improved after Dominic Thiem knocked out Kei Nishikori.
Thiems 6-1 6-4 victory at the O2 on Thursday means six-time champion Federer will top group Lleyton Hewitt if he defeats Kevin Anderson later this evening.
However, the 37-year-old will also qualify for the semi-finals – as the group runner-up – if he takes a set off Anderson and could even progress with a straight-sets defeat.
Federer suffered a shock opening-day loss at the hands of Nishikori before beating Thiem in his second game of the season-ending event.
Seventh seed Nishikori was smashed 6-0 6-1 by Anderson on Tuesday and his struggles continued here as Thiem found an early break.
The Austrian then saved four break points himself before securing a hard-fought hold to lead 4-1.
It was Nishikoris turn to dig deep in the next game and while the 28-year-old saved four break points, he was finally broken again.
Thiem, a former French Open finalist, then served out for the set. The 6-1 scoreline ensured Nishikori had won just one game in his last three sets of tennis.
No.6 seed Thiem lost his previous two games in the tournament but looked to stamp his authority on this match early into the second, creating an early break point.
But Nishikori, 28, held and gradually began to improve as the crowd at the O2 was treated to a much more competitive set.
The score was 3-3 when Thiem again put his foot down, breaking his Japanese opponent to take control of the set.
Despite boasting a winning record over Thiem, Nishikori was unable to break back as his hopes of qualifying for Saturdays semis were dealt a major blow.
All eyes now turn to the final match in group Lleyton Hewitt between Federer and big-serving South African Anderson.