United took the lead in the 26th minute after Perry Kitchen powered home Taylor Kemp’s corner.
They extended their advantage midway through the second half and it was Kitchen in on the act again, firing Chris Rolfe’s pass into the back of the net.
However, the visitors were back in the match just a minute later through French defender Damien Perrinelle’s header and they grabbed a point with just minutes remaining as former Charlton and Leeds winger Sam pounced on an error from goalkeeper Bill Hamid to level the scores.
Elsewhere, Philadelphia Union also left it late as they claimed their first win of the season with a 2-1 victory over New York City.
Sebastien Le Toux created the opener for the Union, with Zach Pfeffer bundling the ball home, before former Barcelona star David Villa levelled the scores in the 55th minute.
But Vincent Nogueira stole all three points in the second minute of injury-time after City goalkeeper Josh Saunders failed to deal with Andrew Wenger’s cross.
It was a bad night for Montreal Impact as they suffered a 3-0 defeat at the hands of the Houston Dynamos.
Former Derby midfielder Giles Barnes opened the scoring in the 15th minute with a glancing header before Ricardo Clark doubled his side’s advantage with just under 18 minutes remaining.
Substitute Rob Lovejoy rounded off a good night for Owen Coyle’s men with a superb long-range effort.
San Jose Earthquakes also had the winning feeling in Week Five of the MLS after Sanna Nyassi’s 75th-minute strike secured a 1-0 win over the Vancouver Whitecaps.
Nyassi smashed home a left-foot strike from near the penalty spot after the MLS leaders had blocked two previous attempts.
Pedro Morales and Adam Jahn were both shown red cards with just two minutes of normal time remaining after the pair clashed, but it was not to affect the scoreline.
New England and Columbus played out a 0-0 draw, while Sporting Kansas City were held to a goalless draw against Real Salt Lake.