Reading took the lead just after the hour mark thanks to Natasha Harding. Harding's headed effort came from a corner after Mary Earps made a superb save.
Danielle Carter doubled the Royals' lead shortly after Harding put them ahead. It was a wonderfully whipped in free-kick by Emma Mitchell which Carter powerfully headed past Earps, the United keeper had no chance of keeping it out.
Story of the game
United got off to a bright start with Christen Press locking in from range as she tested the Reading keeper. Press was involved in United's best piece of play in the first-half as she pulled off a wonderful flick to put Ella Toone in on goal. Toone played the ball out wide to Kirsty Hanson who put it in the box for Toone to strike and her effort struck the post.
Reading had a great chance to take the lead when Carter flicked on a header towards Rachel Rowe. Rowe picked up the ball, dribbled past the United backline but could only force Earps into a routine save.
At half-time the sides were level.
Jackie Groenen came off the bench and made an impact immediately. Groenen pushed her side forward and started to connect the midfield to the attackers. Leah Galton had a glorious opportunity to take the lead early in the second half but her left-footed volley was well saved.
Angharad James' volley for the Royals required some fast reactions from Earps to put the ball out for a corner. Harding, the Reading keeper won the header to put the ball past Earps and into the back of the net.
Moments later, it was Carter who doubled Reading's lead. A free-kick from the left hand side was whipped in with venom from Mitchell and Carter headed home with great power past Earps.
United pushed for a comeback but could not mount anything that threatened Reading's goal. Reading held on and completed what was a relentless defensive display as well as being ruthless in front of goal.
United first loss at home in league since in over a year
The Royals managed to pull off a massive upset and handed Stoney's side their first loss since Bristol City beat them 1-0 in January, 2020. United now trail Chelsea by three points at the top of league as well as the league leaders having a game in hand.