The only goal of the afternoon came after 53 minutes when Troy Deeney rose to head home a Juraado cross for the Premier League new boys.
In the final minute, United were inches away from scoring a deserved equaliser when impressive substitute Blair Spittal crashed a shot narrowly wide of the far post.
St Johnstone also suffered a 1-0 reverse when former Dundee midfielder Jim McAlister secured a victory for League One Blackpool at McDiarmid Park.
Despite losing the match, Saints will take the positives from a match they controlled for long periods as they look ahead to next weekend’s league opener at Tynecastle.
Hamilton Accies ran out comfortable 5-0 winners against Maltese Premier side Floriana in a match played in searing heat.
Accies led by two goals at the interval, following a strike from the edge of the penalty area from Ali Crawford (29) before Christian Nade doubled the lead eight minutes later with a drive from 20 yards.
Hamilton skipper Darian Mackinnon netted 40 seconds into the second half from close range and a header from Lucas Tagliapietra (48) and a Dougie Imrie goal completed the rout.
Kris Boyd scored two and set up the other goal as Kilmarnock beat Fleetwood Town 3-1 at Rugby Park.
Boyd, in his third spell at Killie, pounced in the opening minutes from close range after Kallum Higginbotham and Josh Magennis had combined.
Amarei Bell drew the English League One side level when he ran in on goal and blasted his shot past Jamie MacDonald.
Boyd restored the lead on 69 minutes before he set up Chris Johnston to place the ball under the Fleetwood ‘keeper to complete the scoring late on.
Partick Thistle were held to a 1-1 draw by English Championship side Rotherham at Firhill.