Defending champion Angelique Kerber has already survived two testing encounters during Australian Open 2017, losing the second set in her matches with Lesia Tsurenko and Carina Witthoeft. However, she is likely to face an even more difficult challenge when she comes up against Coco Vandeweghe in the fourth round.

The American, 25, has made an impressive start in Melbourne. She produced a typically aggressive display of big-hitting to dispatch 15th seed Roberta Vinci in straight sets in round one, then also beat Pauline Parmentier in straight sets in round two despite a more patchy performance.

However, the most significant victory Vandeweghe has earned so far was over Bouchard in round three. She was superb in the opening set of the match as she hit five aces and 12 winners (while making only one double fault and eight unforced errors) to take it 6-4. But the American’s level then dropped and the Canadian hit back to win the second set and surge into a 4-2 lead in the decider.

At that point, Vandeweghe could have accepted that even though she had started the match well, Bouchard had produced a good comeback and the match had got away from her. However, that kind of approach is not in the American’s DNA. She is determined and aggressive and she does not fear any player or situation. So she rolled up her sleeves, made the Canadian play extra shots in her next service game and got the break back she needed to make it 4-4. Four games later, Vandeweghe broke Bouchard again, sealing match point with an excellent backhand winner.

It is clear that the American has the game to upset Kerber. She also seems to be in the mood to go far at this year’s Australian Open. Throughout her match with Bouchard, Vandeweghe was constantly firing herself up and trying to coax out her finest tennis. It worked in the first set, and it helped her get across the line in the final set. If she is as focused and determined when she plays the German, the world number one will need to play very well to win.

Kerber is capable of overcoming all the challenges Vandeweghe might pose – but she will need to be close to her best. She has always been a great defender and counter-puncher, and there is no better example of her abilities than her victory over Serena Williams in last year’s final. When you consider Vandeweghe’s strengths, that performance seems even more relevant. Like Serena, the world number 35 has a huge serve that earns a lot of easy points. Also like Serena, Vandeweghe hits powerful groundstrokes off both wings and usually produces a large number of winners when she performs well. Given these strengths, perhaps Kerber should consider employing a similar strategy to take on the lower-ranked American to the one she used in the 2016 final.

The most likely outcome of this entertaining-looking fourth-round match is a Kerber victory. However, if her level drops, Vandeweghe will probably win at least one set. And, if the American plays to her very best, she could pull off an unlikely win. Considering this potential for an upset, the defending champion should go into the match with the expectation that she will need to produce some of her best tennis to win.