This time last year, none of the semifinal pairings were regular teams. Chan Yung-Jan and Martina Hingis began their partnership in February and have won six titles since then; Sania Mirza and Peng Shuai are playing just their third tournament together, having teamed up at the start of the hard court season and scored a quarterfinal in Toronto and semifinal in Cincinnati.
Lucie Hradecka and Katerina Siniakova had played and lost one match together in the Midland $100,000 ITF event in 2014 before teaming up regularly in January. Meanwhile, following the horrific knee injury suffered by her usual partner Bethanie Mattek-Sands at Wimbledon, World No.1 Lucie Safarova has resumed a partnership with Barbora Strycova - previously only seen in Fed Cup and their bronze medal run at last year's Rio Olympics.
Consequently, in neither semifinal have the teams previously faced each other as teams. Of particular interest, though, is the fifth match between Martina Hingis and Sania Mirza since the three-time Slam-winning duo split at the end of 2016. Hingis and new partner Chan have beaten Mirza three times - alongside Barbora Strycova in Indian Wells, Yaroslava Shvedova in Rome and Kirsten Flipkens at Wimbledon. Mirza and Strycova gained some revenge by reversing the Indian Wells result two weeks later in Miami.
Lucie Hradecka and Katerina Siniakova's partnership has garnered four finals in 2017, in Taipei, Indian Wells, Charleston and Prague, along with a Roland Garros semifinal - but they are yet to win a title together. The Czech pair entered the US Open having suffered first-round exits in both of their hard court warm-ups.
The all-Czech semifinal in the top half contains two US Open titles and a further final between them. Lucie Safarova is the defending champion; last year, with Bethanie Mattek-Sands, was the first time she had got beyond the third round here. Lucie Hradecka took the trophy in 2013 and the runner-up plate in 2012, both alongside Andrea Hlavackova. Meanwhile, Barbora Strycova is playing her third Slam semifinal and second in Flushing Meadows, having reached the final four with Kimiko Date in 2014; and Katerina Siniakova is also playing her third Slam semifinal, but first in New York.
Martina Hingis is the most decorated player in the bottom half, having first won the US Open doubles crown in 1998 with Jana Novotna and again in 2015 with Sania Mirza. The Swiss player also reached the final in 2014 with Flavia Pennetta, and today marks her seventh semifinal in Flushing Meadows - the first having come all the way back in 1996 alongside new Hall of Fame nominee Helena Sukova.
Sania Mirza is the only other previous champion in the bottom half. The Indian player also reached the semifinals here in 2013, with Zheng Jie, and 2014, with Cara Black. Chan Yung-Jan is playing her third US Open semifinal, having reached the final on her debut as an 18-year-old in 2007 with Chuang Chia-Jung and another semifinal in 2010 with Zheng. Peng Shuai, meanwhile, is playing her first career US Open semifinal in doubles following quarterfinals in 2004, 2012 and 2013.
Lucie Safarova, the Australian Open and Roland Garros champion alongside Bethanie Mattek-Sands, is the only Slam titlist this year remaining. Peng Shuai, runner-up in Melbourne with Andrea Hlavackova, is the only other semifinalist who has reached a major final in 2017.
In mixed doubles, Martina Hingis and Jamie Murray remain undefeated. The Wimbledon champions' winning streak has been extended to eight here.
Sloane Stephens, the lowest-ranked of the four semifinalists, is now in her first Slam final. Positivity has paid off for Stephens 2.0, argues Bryan Armen Graham in The Guardian.
Stephens and Madison Keys broke through to their first Slam semifinals four and two years ago respectively - but only now are they fully ready for the spotlight, says Helene Elliott at the LA Times.
Relive highlights of last night's semifinals.