CINCINNATI, OH, USA - Lesia Tsurenko has shocked No.7 seed Garbiñe Muguruza in the second round of the Western & Southern Open, coming from a break down in the deciding set to end the defending champion's 2018 campaign with a seesawing 2-6, 6-4, 6-4 victory in exactly two hours.

The result marks Tsurenko's sixth career Top 10 win, and first since she ousted Lucie Safarova from the 2015 US Open in the first round - the same year as her sole previous win over Muguruza, a 7-5, 6-1 triumph in Toronto. Having been forced to retire two games into their fourth-round encounter at Roland Garros this year with a hamstring injury, the Ukrainian now levels the head-to-head at 2-2.

The Spaniard had been sidelined from the US Open Series thus far due to an arm injury that forced her to withdraw from San Jose and Montreal, and today marked her first match since her Wimbledon title defence came to an end in the second round at the hands of Alison Van Uytvanck.

"I think it was a very ugly match, but I'm happy that I fought," Muguruza said after the match. "You know, the level wasn't very high, but at the end she managed to come back in the third set and play better and found a way to keep winning and win the match.

"I felt good. I'm happy that I didn't feel pain. Obviously I didn't have a lot of practices to try to recover, so I had to manage a little bit. I'm happy that I didn't felt pain. I competed. It didn't go my way. I'm going to take that positive and keep training for US Open."

Muguruza was forced to save two break points in the very first game thanks to three unforced errors; in the next game, she spurned three of her own before Tsurenko's clean hitting on the backhand and the serve came into its own.

Indeed, through the first four games it was Tsurenko who had greater control over her form, with her backhand down the line particularly sharp; in the fourth game, she would hold thanks to a brace of excellent improvised shots when seemingly on the back foot.

But Tsurenko was unable to get the ball back into court on the biggest points. Though Muguruza's ground game was patchy, her serving was on point: a third break point at 2-2 was staved off with a third service winner, and the two-time major winner held with an ace.

It was at this point that Tsurenko's own groundstrokes began to go awry. Three unforced errors - there would be 15 in total across the first set - opened the door for the former World No.1 from 40-15 up in the next game, an opportunity she seized with relish with an inside-out forehand winner.

Even the Acapulco champion's trust backhand was letting her down now; two games later, serving to stay in the set, another three mistakes off that wing paved the way to another break, with one in the net sealing the set for Muguruza.

The Roland Garros semifinalist's serve had been clutch in the first set, but the second saw this reversed entirely. Two break points in the third game were saved with service winners, as had become routine. A third almost was, but a Hawkeye challenge led to a replayed point - and a double fault. These would mount up for Muguruza, with another two back-to-back conceding another break of serve in the seventh game as her tally reached seven.

Tsurenko was not able to take advantage immediately. The 29-year-old coughed up three easy forehand errors - one long, one wide and one in the net - and a backhand one to lose the first break. But her hold for 3-3 saw the four-time WTA titlist begin to rediscover her clean hitting and ability to sustain rallies - and as Tsurenko's form rose, Muguruza's fell. Racking up 14 unforced errors to just five winners in the second set, the Monterrey champion was unable to peg Tsurenko back again, and the World No.44 levelled the scoreline on her fourth set point after another Muguruza backhand found the net.

As the match headed into a decider, the seesaw tipped once again. A rejuvenated Muguruza came up with a brilliant lob and a swashbuckling smash to hold - and this time, it was Tsurenko's turn to be plagued by double faults, coughing up three en route to losing serve for 0-2.

Muguruza's patch of good form continued through the next few games. A small opening for Tsurenko in the fifth game was snuffed out, with Muguruza storming forward to hammer three drive volleys away - including on break point - to hold from 0-30.

But three careless, errant groundstrokes and, on break point, a ninth double fault provided another plot twist as Tsurenko broke back for 3-4. Thence, the Doha runner-up's errors would come in a cascade, particularly - but not limited to - the backhand. That shot went into the net on break point for Tsurenko to move ahead 5-4; and, despite a window of opportunity as the Ukrainian committed a seventh double fault as she served for the match, it went wide and into the net once again to bring up match point. At this point, Muguruza demonstrated some variety with her mistakes, sending a forehand long - her 43rd unforced error of the day - to cap a hard-fought win for Tsurenko.