On the tenth day of the US Open, they would meet for the fifth time and third on hardcourts. Coco Vandeweghe, the twenty-five-year-old American and #20 seed, defeated the reigning world #1 and 2016 Open finalist, Karolina Pliskova 7-6, 6-3 to reach her first semifinal at Flushing Meadows.

For both, there was plenty on the line. Earlier this season, Coco had succumbed to the pressure of expectation at the other three slams while Pliskova sought to validate the number one ranking she first attained this past July and equal or surpass her second-place finish last year.

Both are known primarily for their powerful serves and penetrating groundstrokes. The key to victory would be winning percentage on second serve points and in turn, break point opportunities/conversion. Vandeweghe correctly predicted that the serve ultimately would determine the outcome of the match for she chose to receive after winning the toss.

In the third game of the first set, Pliskova found herself down triple break point after missing a couple of shots. Vandeweghe broke when she hit a blistering service return winner.

Coco, serving up a break at 4-3, threw in two double faults and found herself down break point. Though she managed to get to deuce twice, Pliskova broke back with an amazing forehand winner.

The twenty-five-year-old Czech held for 5-4 and was four points from closing out the set but the American had a few more aces up her sleeve. Despite being down a set point, Coco maintained her focus and aggressive hitting and with a backhand winner down the line, leveled the set at five games all.

Both held easily to 6-6 and would play a tiebreaker to decide the set. Vandeweghe took more chances and continued to strike the ball with authority while Pliskova appeared off balance. The American raced to a 5-2 lead and unleashed on serve to win the tiebreaker 7-4.

Although Pliskova had a considerably higher winning percentage on second serve points in the first set compared to the second, they played a greater number of games, in addition to a tie-breaker in the first set.

In the second set, just as in the first, Pliskova served just one ace and won a negligible 25% of second serve points. Pliskova, the WTA tour leader in aces the last two seasons, was unable to rely on her serve to dictate play and win easy points and in the end, this cost her the match.

Even though Coco’s winning percentage on second serve points was also quite low at 33%, it was considerably higher than Pliskova’s and this was significant. Pliskova lost serve in the fourth game of the second set as Vandeweghe continued to hit out on her groundstrokes as well as finishing off points at the net.

In the following game, the unflappable Czech remained composed and earned three break points the last of which she converted as the American missed several balls long and double faulted.

Recognizing the urgency of the moment and resilience of her opponent, Vandeweghe steeled herself and immediately broke back and would hold for 5-2. Pliskova would hold at love but was just four points from packing her bag.

Serving for the match and her first semifinal at her home slam, Vandeweghe attempted to steady her nerves and continue to swing freely.  With a forehand winner, she was two points from victory but when her next shot found the net, she faced break point. She would level at deuce when Pliskova’s forehand found the net.

Once again two points from victory, Vandeweghe uncorked a scorching crosscourt forehand winner to reach match point. Denied on her first opportunity to close out the match, she prevailed on the second when she struck a magnificent forehand winner down the line.

Although Coco produced more errors than winners, she remained aggressive and never took her foot off the gas. She demonstrated a drastically improved mental clarity and for the most part, played within herself.

It remains to be seen whether this high-risk style of play will continue to pay dividends when she faces the #15 seed, Madison Keys. This is the first time since 1981 that four Americans will compete for a place in the finals. Now that is something to write about.