Two good friends stepped inside Arthur Ashe Stadium on Wednesday, but only one could emerge as a first-time Grand Slam semifinalist.
That woman was No. 13 seed Belinda Bencic, who followed up a Round of 16 upset of defending champion and world No. 1 Naomi Osaka with a 7-6, 6-3 win over No. 23 seed Donna Vekic to move into the final four at the US Open.
The Swiss, who first reached the US Open quarters five years ago as a prodigious 17-year-old, broke Vekic when she served for the first set before winning a tiebreak, and won the last four games of the match to seal her personal milestone in one hour and 42 minutes.
In some ways, Bencic, one of the WTA's elite counterpunchers, had the perfect preparation for her second Open quarterfinal by deftly directing Osaka's booming groundstrokes around the court for her third win over the Japanese in 2019.
In what was a chess match of sorts between the Swiss and Vekic, who is more traditionally aggressive, the two players swapped service holds over the first eight games of the first set, with neither even getting a look at a break point opportunity.
"I knew today was going to be a very difficult match. Donna is in great form now. She showed it again today," Bencic said. "I think we played a very good match with high-quality rallies. It was definitely not easy. I'm happy. I don't know, I stayed calm in the important moments. I just managed to win." 
Fast forward to 2019. In her main-draw debut at the US Open, the fiery 15th-seeded teen has advanced to her first career major semifinal.
The 19-year-old Canadian overcame an error-strewn first set and used her superior firepower to came back to beat No. 25 seed Elise Mertens, 3-6, 6-2, 6-3, on Wednesday evening.
“This is honestly so crazy,” said Andreescu. “What I’ve accomplished this year, I’m honestly speechless. I need someone to pinch me right now.”
“Is this real life?” she asked the night crowd.
In the opening set, the 5-foot-10 Mertens, a smooth ballstriker from Belgium, was impenetrable from the backcourt. Andreescu struggled to find her timing and range, misfiring with her heavy ground strokes.
But in the second set, the young Canadian quickly turned things around. She began to mix things up, alternating power with net approaches and deep, looping shots to throw Mertens off her rhythm. Andreescu broke Mertens three times, winning 17 of the last 21 points, and rolled through the second set.
The third set remained close, until Andreescu stepped on the gas at 4-3. She broke serve for the fourth time in the match with a powerful backhand return down the line for a winner.
It was the decisive advantage she needed to close out the match and push on into the semis.
