"It was a tough day," said the fly-half whose former clubs include Swansea, Neath, Grenoble and Doncaster Knights. "But we stayed positive and concentrated on what we wanted to achieve. We did ourselves proud on Saturday and now we want to build on that in our next game at Ayr this weekend."
Rees slotted five penalties and two conversions at Clifton Lane, while Damien Welch, Nathan Bowen and Matthew Jacobs ran in for tries. Rees added, "The game was won upfront - we knew Rotherham would pose a forward challenge but we met that challenge and dominated the game throughout. Rotherham found it difficult to break down our defence and we scored at the right times. I was happy with my game too. Obviously, the win was the priority but hopefully if I kick well, it gives the boys a bit of extra confidence."
Rees, who experienced European rugby with Aberavon, Neath, Swansea, Bridgend, Grenoble and Albi enjoyed the cross-border atmosphere. "Rotherham had a good crowd which made it an exciting affair. It was our first competitive cross-border match and I think we may have proved a few people wrong but there will be added expectations of us now.
"Ayr is a game that we can win but we are taking nothing for granted and we are conscious they are a good side and will be playing at home which will make for another big challenge.
"We had a lot of young players in our side on Saturday and they are developing very quickly in this competition. We are hoping the confidence gained in the British and Irish Cup will give us a boost when we return to the Principality Premiership later this month."
Welsh Clubs in British & Irish Cup action this weekend
Saturday, 18 December
Ayr v Llandovery (3pm)
Llanelli v Nottingham (3.30pm)
London Welsh v Swansea (1pm)
Pontypridd v Birmingham & Solihull (2.30pm)
Plymouth Albion v Newport (3pm)
Sunday, 19 December
Neath v Bedford Blues (2.30 pm)