For the second night in a row, the end of The Tennis Podcast had to be recorded at past 2am in New York.That’s because Rafael Nadal and Dominic Thiem played a marathon match long into the night, with Nadal prevailing in a thrilling deciding set tiebreak.This was tennis at its absolute best, say David and Catherine, and also a brilliant advert for fifth set tiebreaks.Nadal will now face Del Potro in a repeat of last year’s semi-final. Del Potro beat Isner in a match that played out as most people expected. Is there an irresistible force behind Del Potro pushing him to the title?Elsewhere, there was a big surprise in the opening match of the day when Sloane Stephens was beaten in straight-sets by Anastasija Sevastova. How did Sevastova “bamboozle” the defending champion? Did Stephens show mental weakness?Will Sevastova’s variety and court craft trouble Serena Williams in the semi-finals? Serena was a comfortable winner against Karolina Pliskova on Tuesday night. How well did she play?There will be daily editions of The Tennis Podcast throughout the US Open fortnight. The Tennis Podcast is produced in association with the Telegraph and sponsored by Amazon Prime Video, the new home of the US Open in the UK.  See acast.com/privacy for privacy and opt-out information.