It also leaves Watford in deep trouble at the wrong end of the table.
Malkay Mackay's men sit one point ahead of Crystal Palace, who occupy the third and final relegation position following their 1-1 draw at Middlesbrough.
Left-winger Ross Wallace had an early chance for the hosts when he found space in the middle before letting fly from distance only to see his effort deflected through to Watford goalkeeper Scott Loach.
Soon after, Paul Coutts played the ball to right-back Billy Jones but his ball across the penalty areal was deflected against the post.
The visitors responded and Lloyd Doyley's cross took a big deflection off Jon Parkin's head and landed in the path of the unmarked Jon Harley at the back post.
Luckily, Preston keeper Andy Lonergan was quick off of his line and superbly saved from point-blank range after 26 minutes.
An outswinging corner taken by Cleverley led to Martin Taylor having a shot saved after 31 minutes as the Hornets forced the issue.
They made it 1-0 in the 35th minute when Heidar Helguson flicked the ball into the path of Will Buckley.
The forward skipped a Youl Mawene challenge and hit a powerful shot from close-range into the top left corner.
Preston were handed a blow when Chris Sedgwick limped off with a knee injury in the 38th minute and was replaced by Keith Treacy and it was the substitute who played a part in their equaliser soon after the re-start.
Treacy crossed for Preston captain and man-of-the-match Callum Davidson to plant a firm header beyond Loach in the Watford net as they restored parity.
In the 68th minute referee Rob Shoebridge handed Wallace his tenth booking of the season for unsporting behaviour and the winger will now be suspended for two games.
With time running out, Preston huffed and puffed but couldn't find a match-winner, and the points were shared in Lancashire.