The 20-year-old striker has made six Sky Bet Championship appearances for United, all from the bench, totalling 93 minutes.
He replaced Mark Harris after 64 minutes at home against West Bromwich Albion this afternoon, and popped up with a stoppage time leveller.
A long throw-in from Will Vaulks was flicked on by Elliott Moore to the path of Scarlett, who in turn headed beyond Alex Palmer to salvage a 1-1 draw for the U’s.
United head coach Buckingham said: “We’re happy that we’ve come up against a really good side in West Brom, a team that I’m sure will be challenging to go up and out of this league, and to be able to put on the second half performance that we did and come away with a result against a very good team, I’m very happy.
“We made some changes. You saw quite a few in the second half. Louie Sibley came on with Dane Scarlett, and you saw Owen [Dale] and Malcolm [Ebiowei] come on.
“We wanted to really get after them and get more attacking players on the pitch. It paid off, and Dane’s been very patient.
“He’s had probably fewer minutes than he’d have liked, but Mark Harris has been in extremely good form.
“What we’ve now got, including Will Goodwin, is three there, so if we know it’s not quite working with Sparky, then Dane is more than capable of going in to contribute.
“It’s about time one of those long throws came in. We don’t use them very often, so it’s nice to see.
“Pricey [Lewis Price, goalkeeping coach] will be claiming it as a set piece goal, and we chucked an extra body in the box because of the time, and Elliott did really well to flick it on, and I’m really delighted for Dane.”
Buckingham added: “We knew coming into this level of football that we’re probably going to come up against teams that are not better than us, but will pose different challenges.
“We just need to set our team up to be respectful of that, but not come too far away from allowing us to play the way we want.
“What I’m really happy now with is 10 games in, we’ve faced 10 very different tests, but we’ve been able to navigate our way through them to come out with results.
“It’s results at the end of the day which are going to keep us where we want to be, which is in this league.
“If we can keep performing to the levels we have, that’ll put us in the best spot.”