United ended 2018 at Glanford Park with three points after Kyle Wootton struck in the first-half.
Alnwick also had to make impressive saves to ensure the Iron confirmed their victory.
Speaking to iFollow Iron, the 25-year-old said: “It’s a massive win. We’ve been on a poor run for a long time, but we got the clean sheet and the lads hung on for their lives.
“They (Wycombe) showed at their place they were a threat and we dealt with everything they threw at us this time.
“It was such a relief when the final whistle blew, but hopefully we can build on it now.”
The goalkeeper was also pleased that the Iron got the game’s first goal and managed to hold onto that lead.
He said: “We know that when we go ahead, we are a good side. It allows us to get that extra little bit of confidence and the defenders can tighten up a little bit knowing we’ve got that lead.”
Alnwick had to make a superb reaction save in the second-half when he flew across his line to keep out Scott Kashket from close range.
That save, amongst overs, helped the goalkeeper record his third clean sheet in an Iron shirt.
“Their efforts that they had were outside of the box and we defended really well,” said the on-loan Rangers player.
“For the one in the second-half, I need to see it again.
“It is a cross that I could have come for or one that Cam (Cameron Burgess) can head, but I threw myself at the shot and I got something on it.
“We need things to fall for us and I need to make big saves like that, and hopefully I can continue to do that.
“We need more clean sheets, but they are always good to get. That clean sheet feels extra special after the bad run and the type of opponent we were up against. It was brilliant.”
Next up for Scunthorpe is an away trip to Peterborough on New Year’s Day.
Providing a short preview, Alnwick said: “It is a tough period with games coming thick and fast, but after a win you want a game straight away to keep that run going.
“We’re not going to get carried away, we know they’re a good attacking side, so it is down to us to defend well again and hurt them going forward.
"If we can grind out a result down at their place, it will be nice for the New Year.”
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