O'Connor kept his cool to cancel out Massimo Luongo's 70th minute-opener as his thumping finish with 90 seconds to go set the tie up perfectly for the second leg at Griffin Park on Monday. It was rough luck for Tottenham loanee Luongo, who went from hero to villain as he made the crucial foul at the end of Brentford's best move of the night.
"Kevin is excellent," the German manager said. "He had not played for a long time but stepped up to the plate. Obviously, in the end, he used all his experience and skills to convert the penalty and I'm very happy for him."
He added: "It was a difficult situation for him as he was not playing many matches, but in all the games he looks very solid and does a great job."
In a match of few chances, Brentford created very little going forward until substitute Harry Forrester was fouled deep into added time.
The best chance for the visitors in the previous 90 minutes fell to Adam Forshaw who really should have opened the scoring.
Slipped through expertly by Bradley Wright-Phillips, the former Everton man rolled a low left-footed shot across goal when one-on-one with Wes Foderingham. And with the sides ultimately cancelling each other out, Monday's second leg looks set to be a tight affair.
"The tie is wide open and I said before the game, we must make sure it was," Rosler added. "To get a draw after all the circumstances of last week was a very good result. It was a difficult game with not much between the two teams. In the first half they pushed us back but we had the best chance."
Swindon boss Kevin MacDonald had few arguments about the result and reinforced his opposite number's belief that there is very little between the two teams.
"The timing of the goal is obviously disappointing but it is 1-1 and we are both in the tie," he said. "I thought the conditions were difficult for both teams. No team really handled it in the way they'd have liked to. I think both teams were nervous as well as it was a big game."