Oxford manager Chris Wilder has urged his players to "finish the job" after reaching their first play-off final.
United face York on 16 May at Wembley in the Blue Square Premier promotion final for a spot in the Football League after beating Rushden 3-1 on aggregate.
Wilder told BBC Oxford: "I thought the players were fantastic from the first minute. We deserved to go through.
"I want them to enjoy these days - we want more of these. We've got to make sure we finish it off now."
He continued: "I thought in the first 15 or 20 minutes we were dominant without finishing it off.
"The support is absolutely phenomenal. We just want the fans to have a day out and make sure we win. The players have been first class all season.
"We've had a lot chucked at us but we've got a plan and we'll try to stick to that plan and try to finish it off."
Chairman Kelvin Thomas said: "We're not finished yet. We've got to make sure we finish the job. It's great for the fans to enjoy the experience. There's nothing you can say went wrong today - it all went so well.
"I was nervous from the start but we've proved as a club and as a team we can handle the big occasion."
United drew the first leg 1-1 but won Monday's home leg 2-0 with goals from Matt Green and James Constable.
We had to battle hard - the back four and the keeper were amazing and they deserve a lot of credit as well
Top scorer James Constable
Before the first leg, Diamonds defender Kurt Robinson had said that Oxford's strikers were "nothing special".
And Constable said: "That played in the back of our mind. It was something we'd seen before the first game. We remembered it and went to put those comments right. I'm delighted with the win."
The 25-goal striker, who lost at Wembley in the 2007 FA Trophy final with Kidderminster, said: "It's going to be an amazing feeling. There'll be more fans than we [Harriers] took. I'm desperate to put that defeat right.
"It's a massive game. We knew it was going to be a big game today. The fans were amazing, and that was for them - a bit of success. We can go to Wembley full of confidence that we can bring the trophy home.
It's one step closer to getting the big prize we all want. It's great for the fans and players and everyone involved
Midfielder Simon Clist
"We had to battle hard - the back four and the keeper were amazing and they deserve a lot of credit as well."
Early league pacesetters Oxford topped the table by eight points at one stage this season, before letting the advantage slip and eventually finishing third.
And Constable said: "It's massive for the club. It's a chance you don't often get. We knew the position that we were in earlier in the season, and we maybe let it go slightly so we're absolutely desperate to put that right."
Green, who scored the opening goal on Monday, said: "Words can't describe how I felt. It was amazing. Money can't buy it; it was the best feeling in the world."
The striker, on loan from Torquay, was on the bench last season as the Gulls won promotion to the Football League.
He said: "Last year I didn't get a minute on the pitch - all you can do is put on a brave face. It's a once-in-a-lifetime opportunity. There's Premier League players that don't get to play at Wembley."
Midfielder Simon Clist, who set up Green's opener, is wary of the task yet to come for United.
He said: "It's one step closer to getting the big prize we all want. It's great for the fans and players and everyone involved.
"We haven't won anything yet. We've still got to prepare right. Tomorrow we get our minds back on what we have to do."
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