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Aryna Sabalenka roared back from a slow start to beat Coco Gauff 7-6(5) 6-2 and clinch a semi-final spot at the season-ending WTA Finals, sending the defending champion packing and assuring Jessica Pegula of a place in the last four. The world number one, who is seeking a maiden trophy in the event since a run to the final three years ago, finished top of the Steffi Graf Group and next takes on Amanda Anisimova in a rematch of their US Open title clash. "She always makes me work hard, always great battles against her," Sabalenka said about Friday's showdown. "I enjoy playing against her and I enjoy the fights so I'm excited to play her. I hope it's going to be a great match." American Pegula meets the in-form Kazakh Elena Rybakina, who qualified for the semi-finals as the best player from the Serena Williams Group to continue her own bid for a maiden trophy in the season finale in Saudi Arabia. Gauff's erratic serve had been a concern after her opening defeat by Pegula, but it was the 21-year-old's aggressive return game that stood out against Sabalenka as she broke to start the match and went 4-2 up at the King Saud University Sports Arena. Sabalenka let out a scream after she saved break points and held for 3-4 in the rematch of the French Open title clash that she lost, and the fired-up Belarusian soon broke to draw level at 5-5 with a neat forehand winner. "I probably wouldn't put myself in that situation (again)," Sabalenka said about being 4-5 and 0-30 down. "I was just trying to stay aggressive and trying to find my rhythm. I was working for the second set already, but magically I was able to turn things around. "I'm super happy with the performance and super happy to get this win in straight sets." Sabalenka showed more fight in the tiebreak to come from behind and take the first set, and there was no stopping the 27-year-old when she eased to a 4-0 lead in the second set.