The League One side had the majority of the possession and created the better chances, but Walsall, – with Clarke at the heart of their defence – shut the visitors out.
That was until the 84th minute when former Wolves winger James Henry was the first player to latch on to a low cross, turning home the only goal of the game in front of the visiting supporters.
And centre-back Clarke felt Oxford were more ruthless.
“We came out with a game-plan,” he said.
“We knew they were a possession-based team and they would have a lot of the ball.
“It was more of a counter-attacking thing (for us). We had some really cutting-edge chances but unfortunately when it comes down to it, it was about being better in both boxes. They were more ruthless in our box than we were in theirs.”
But the 30-year-old was full of praise for his manager after the final whistle.
“The way the gaffer is, he’s very level headed,” Clarke added.
“He’s always said to me that you have to treat each game as it comes. Don’t worry about the next one thinking ‘we have to win that’, we go out to win every game.
“I’ve never known him to rest someone thinking ‘we’ll take what we can out of this game’ – he goes to win every game.
“That’s how you become a winner I think.
“Building wins upon wins and taking each game as it comes.
“If you start looking at where you are, looking at other games, you’ll try to pick ones you might win.
“We try to win every game and that’s the way forward.”
The defender joined the Saddlers in the summer from Clarke’s old club Bristol Rovers, and he says it was loyalty that made him follow his manager to the Black Country.
“You can put it down to loyalty really,” he said.
“He took me off the building site, a couple of times now actually.
“He’s a great bloke, an honest bloke.
“If I aspire to be a manager then that’s what I’d want to be.
“An honest bloke, hardworking.
“That suits me down to the ground, playing for him.”