Clarke has played every single minute of league football since the U’s won promotion back into npower League Two, but a knock picked up last Monday ruled him out of Saturday’s clash with Gillingham.
It opened the door for Brown, whose only two appearances for the U’s this season have come in the Johnstone’s Paint Trophy.
The 35-year-old’s last first-team outing was way back in November and lasted just 12 minutes before being sent off, meaning this was a first Oxford clean sheet.
While admitting to feeling a few butterflies before the game, Brown was completely unfazed at being thrust into one of the biggest games of the season.
“I enjoyed it, it was a bit better than the JPT,” he said.
“Don’t get me wrong, I was nervous since I knew Clarkey was injured.
“I thought ‘now’s the time to prepare right’ so I did everything I used to do.
“I’ve been in a comfort zone all season thinking Clarkey’s not going to get injured, so I’ve been doing pretty much what I want really – obviously training well, but I didn’t have the added pressure of playing first-team football.
“But when it came to it I got my head on it last week, ate right, prepared right and got mentally sound.”
On the day Brown had little to do as Gillingham’s dangerous forward line was kept quiet in the 0-0 draw.
The veteran had to wait until the final minute of normal time to be tested, when he turned a shot from Chris Whelpdale around apost.
Brown, who spent a year playing in South Africa with SuperSport United before signing last summer, was happy to keep the effort out en route to a clean sheet.
He said: “It came off my hand and hit my elbow, it wasn’t technically the best bit of goalkeeping, but I was happy considering I hadn’t played a league game for two years in English football.
“I went to Africa and it was a completely different game, but this was back in the mix of League Two football.
“It was quite kind to me, there were a couple of crosses which I quite enjoyed taking.
“We should have played better and won, but it’s a clean sheet and we’re still in the play-offs.”