The 25-year-old Scot, man of the match in The Tykes' 2-0 home win over Millwall on Tuesday night, also saluted another rock-solid defensive display as Barnsley kept a fourth clean sheet in their last five matches.
"I was so excited for the game and everyone was the same," O'Brien said after the Tykes had secured their fourth win in six matches under manager David Flitcroft.
"The shift the lads put in was unbelievable. The last six games have been incredible with the effort we've put in.
"The lads who played at the back were safe as houses - I don't remember (goalkeeper Luke Steele) Steeley making a save."
Chris Dagnall struck his fourth goal in as many games for Barnsley, while new signing Jason Scotland, who arrived at Oakwell on a short-term deal until the end of the season on Monday, crashed home a goal on his debut, just 90 seconds after stepping off the substitutes' bench.
"You can see Jason's quality straight away," O'Brien added. "He came in (on Monday) and it's not long to bed in.
"He's off to a flyer and hopefully he'll bag a few more. We'll get our energy back. We'll just go again and take each game as it comes."