Swindon started well, and took the lead on 35 minutes with a goal from McGovern. Swindon then went close again before half time, but went into the break winning 1-0.
The second half wasn't so good for Swindon, and Leyton Orient equalised on 67 minutes with a goal from Jarvis.
Then thing went from bad to worse for Swindon on 72 minutes when Alex Revell, who played for Swindon for part of last season gave the London side the lead.
Swindon pushed to get an equaliser, but ran out time and lost the game 2-1, so are no out of the Carling Cup after only the first round.