MALLORCA, Spain - First-round play at the Mallorca Open concluded on Wednesday with another shock as qualifier Alison Riske finished off No.2 seed Angelique Kerber 5-7, 6-2, 6-1 - meaning that five of the tournament's eight seeds have lost their openers, while all six qualifiers have progressed to the second round.

Riske, whose first 13 WTA-level wins came on grass, has long been renowned as something of a specialist on the surface - and despite having to come through the qualifying rounds due to a ranking dip earlier in the year, has rejuvenated her form over the past month. After a maiden clay final in Nurnberg, the American would take eventual champion Simona Halep to three sets at Roland Garros - and subsequently, back on her beloved lawns, would take the ITF $100,000 title in Surbiton and follow it up with a quarterfinal last week in 's-Hertogenbosch.

"I always love playing on grass, it's my favorite time of year," she smiled afterwards. "And I think this is the hottest weather I've ever had while playing on a grass court, so it's been really nice - gorgeous!"

Though Kerber began strongly, breaking Riske in the opening game and building a 3-1 lead, the World No.61 began to find her range after that - setting the stage for an enthrallingly close opening stanza in which seven of the final eight games went to deuce, each player responding to her opponent's strong play by raising her own level.

But although the 2014 Tianjin champion would succeed in levelling the scoreline, breaking Kerber as she served for the set, the German continued to battle hard, eventually taking the set on her sixth set point - and once again seizing the American's serve at the start of the next set.

"It was a tight first set, and I think I just got a bit unlucky," said Riske afterwards. "Obviously she played well, but there were a couple of things I could have done better."

But it was then that Riske's affinity for grass began to show, demonstrating an understanding of the surface's nuances with canny slices and dropshots - interspersed with hard, flat aggressive groundstrokes. The 27-year-old broke straight back, reeling off six of the next seven games to square the match at a set all.

Yet again, Kerber started the third set brightly with a break of serve - but yet again, her lead would be brief. The two-time major champion conceded the advantage immediately - and at this point, play was halted for the day due to falling darkness.

On resumption, Riske was in even sharper form than the previous day. The former World No.36 required just over 25 minutes to motor across the finishing line, winning all five games to 30. Riske took both of her break opportunities on the first go, both with backhand winners, and would prevent Kerber from even reaching game point.

A forehand winner, her 41st of the match, sealed the 12th Top 20 win of Riske's career and second of 2018 following her upset of Caroline Garcia in the second round of Miami. Asked how she had dealt with the postponement afterwards, she explained: "Well, it was really positive. Today we were going to have off anyway, so it wasn't like we were going to have to double up on matches, first of all. And unfortunately we can't control things like that - I was just trying to take a step back and focusing on what you can control, and I thought I did a good job of that today."

It is also Riske's first win over Kerber in four meetings - indeed, in each of their previous encounters, she had not been able to win a set. Her reward is a second-round date with Polona Hercog.