Semifinal day at the Phillip Island Trophy had it all: underarm serves, wild momentum shifts, match point saves. 

When the dust settled, the two lower-ranked players had pulled off upsets, with Daria Kasatkina defeating No.8 seed Danielle Collins 6-1, 6-7(6), 6-2 and No.13 seed Marie Bouzkova erasing a 1-4 third-set deficit and surviving two match points to beat No.2 seed Bianca Andreescu 6-7(9), 6-2, 7-5.

Kasatkina had not reached a final since winning Moscow 2018, a title run that had put the Russian into the Top 10 for the first time. An extended slump since has seen her fall to World No.75 in the rankings, but Kasatkina has quietly put together a 17-6 win-loss record and counting since Rome last September.

2021 Phillip Island Trophy Highlights: Kasatkina holds off Collins for final berth

The 23-year-old twice came within two points of victory in a dramatic second set that featured 10 breaks of serve and the first of three underarm serves Collins attempted over the course of the day. The American wheeled out the surprise tactic at a crucial moment - serving at 5-5, 15-40 - and it paid off by saving that break point, though not the game.

Collins also essayed consecutive underarm serves in her first service game of the deciding set, and was successful with the first but not the second. Indeed, a much-improved serve was ultimately key to Kasatkina's victory. During her 2019 dip, it lost much of its bite and was frequently attacked with gusto, but on Thursday Kasatkina struck 10 aces in total - including two in a row to close out the win.

For Collins, a maiden final remains elusive. The American has now lost all five of her WTA semifinals following Miami and San Jose in 2018, the 2019 Australian Open and Adelaide 2020.

Not to be outdone by the preceding match, Bouzkova and Andreescu delivered a rollercoaster ride that was unpredictable at every turn. It was a reprise of the pair's 2019 Roland Garros first-round tilt, a 5-7, 6-4, 6-4 marathon won by the Canadian in three hours and two minutes. This time round, they were just one minute shy of matching that.

Three-setters are becoming a habit with Andreescu in particular: 19 of the 33 completed matches she has played since the start of Indian Wells 2019 have gone to a decider. The Canadian's record in them is stellar - she has won 16 of those 19 ties - but against the dogged Bouzkova her penchant for taking the scenic route backfired.

Despite losing a 4-0 lead in the first-set tiebreak, Andreescu would still manage to close it out on her fourth set point, saving one against her. But Bouzkova wasted no time in bouncing back to level the scoreboard, and then proved steadier than Andreescu as she edged the final set. The 2019 US Open champion would commit 52 unforced errors over the course of the match, two of which came on both of the match points she held at 5-4 on Bouzkova's serve.

In Friday's final, Kasatkina will bid to lift her third trophy in her sixth career final. Bouzkova, meanwhile, is aiming for her maiden title, having lost her first final in Monterrey last year to Elina Svitolina in a 7-5, 4-6, 6-4 three-hour clash.