The pair hadn't played since the 2012 Rogers Cup, where Barthel pushed Radwanska to a final set tie-break; the German was equally aggressive on Monday, breaking serve three times to capture the opening set.
Though Barthel would hit 35 winners, the former World No.2 hit back with 33 of her own, and kept a far cleaner stat sheet with 13 fewer errors than her unseeded opponent. Quickly leveling the match at one set apiece, Radwanska appeared on course for a smooth victory, but Barthel had other plans.
The German broke serve in the eighth game of the final set and had her chances two games later as she tried breaking serve to stay in the match; Radwanska ultimately proved too strong, serving out her place in the third round.
Up next for the 2012 Wimbledon finalist is WTA Rising Star Madison Keys, who had to work her way through her own three-set affair, defeating qualifier Kateryna Bondarenko, 3-6, 6-1, 6-0. Radwanska leads their head-to-head 4-1, but Keys won their most recent face-off at the US Open, defeating the Pole in straight sets in the third round.