The 20-year-old was drafted in at the back for the Doonhamers’ convincing 3-1 victory at Galabank on Tuesday night.
Dunn never put a foot wrong until he was substituted off during the second period after suffering from cramp.
A delighted QoS boss said: “All the players put in really good performances, individually and collectively.
“Scott played extremely well and was really composed all night. I’m sure that will give him a massive lift. Euan East has been on fire in the past two matches and you would guess he’s played in defence for years.”
And Dunn – who enjoyed a loan spell at South of Scotland side St Cuthbert Wanderers last season – admits it was an enjoyable debut and he nearly capped it off with a goal but his header cracked the post.
Dunn said: “I’m pleased to get my first start and it was good to get the win as well.
“I’m glad to get into the starting line-up and we did well at the back. The experienced boys like Willie Gibson helped me through the game.
“I was in the reserves and out on loan last year so this was a good opportunity to come up into the first team during pre-season.
“I want to play first team football, that’s the dream.”
The manager also praised his side’s goalscorers – Ally Roy and Ruari Paton.
“We could’ve scored five or six in the first half. It was a really good performance.
“It was a great ball at the back post from Lee Connelly and good for Ruari to get his first goal.
“We controlled the majority of the match and Ally scored two really good goals which left the goalkeeper no chance.
“Annan did put us under a little bit of pressure near the end and scored but the boys showed their character to score the third goal which killed the game.
“Willie’s run for the third goal was brilliant. He’s an inspiration to the younger players in the squad.”
Queens travel to Fir Park to take on Premiership outfit Motherwell – who signed ex-Queens striker Connor Shields during the close season – for their third group match on Saturday. Midfielder Calvin McGrory will miss out through suspension after picking up two bookings in past two matches
And the boss hopes his young side – who were without Josh Todd and new signing Alex Cooper against Annan due to niggling injuries – can pick up a positive result.
“Josh was feeling his Achilles and Alex has a calf niggle, we hope to have them back as soon as possible.
“We’re trying to get a few loans and two permanent players in but it is proving difficult. There’s a lot of competition out there. We could get players in but at the end of the day they’ve got to be good enough.
“It’s going to be really difficult against Motherwell. We’re building up and getting ourselves ready for the league games but we’ll aim to put in a good performance and hopefully get a positive result.”
Meanwhile, striker Roy admits his superb cup double against Annan has put a “spring in his step”.
The 24-year-old forward netted his first two goals for the Doonhamers on Tuesday and the ex-Airdrieonians man is hoping he can continue his goalscoring form against Graham Alexander’s men.
Roy said: “It’s a brilliant feeling to get off the mark quickly. The header was a good way to introduce myself to the supporters. It puts a spring in your step and boosts the confidence. The challenge now is to keep it up.
“I want to play and score as many goals as I can for the club. I don’t set myself a goal target, I just want to have a good season.
“Our next match is against Motherwell at Fir Park so we know it’s going to be a tough one but we’ll take the confidence from Tuesday’s win into the match. Then we play my old side Airdrie, it’ll be good to see some of the boys again.”