According to The Mirror, Swift joined Hazza at an exclusive after party held at a hotel in the Big Apple, where the popstar pair joined Styles' bandmates for a karaoke session.
Inside the get-together, photos were snapped of Swift - emerging on Twitter via @1DUpdatesAU - along with Harry and his fellow 1D singer Niall Horan and pal Ed Sheeran on stage, where they reportedly sang I Want It That Way by the Backstreet Boys.
The Sun also reports that the group performed a rendition of the Kenny Rogers and Dolly Parton classic Islands In The Stream, with a source also noting: "It was brilliant. There was a huge cheer when they got up."
Zayn Malik's girlfriend, Little Mix star Perrie Edwards, was also thought to present at the bash.
The Mirror adds that Haylor left the bash together at around 3:30 a.m, with The Daily Mail reporting that they were spotted holding hands when they arrived at her hotel.