Orlando City remain without a home win since their introduction to the MLS after Luis Silva's stoppage-time goal gave DC United victory at the Citrus Bowl.
The Floridians tried to force an early breakthrough and almost got it when Amobi Okugo's header from a Brek Shea corner was only inches away from nestling in the back of the net.
Orlando's best chance of the opening period came when another cross from Shea found its way to Kevin Molino before the Trinidad and Tobago international rattled the woodwork, with keeper Bill Hamid beaten.
Hamid was called upon moments later after Darwin Ceren found Rafael Ramos, but the Portuguese defender was denied by the DC shot-stopper from close range.
United almost found a goal of their own when Chris Pontius's shot was cleared off the line by Shea.
City star Kaka tried to find a winner for the home side, only to sky his 78th-minute effort from the centre of the penalty area.
Orlando's wasteful touch in front of goal was punished in the first minute of injury time when Silva popped up to beat Donovan Ricketts and seal victory for United, who are only behind Eastern conference leaders New York Red Bulls on goal difference.
