And Rowntree knows better than most that a strong showing and a positive result could have massive implications, both for individual players and for the squad as a whole.
The former Leicester and England prop played for the Lions in their mid-week match in between the first and second internationals in 1997 as the tourists thumped Orange Free State 52-30 before going on to see off the Springboks 18-15 four days later.
A full handful of players who featured in that commanding win in Bloemfontein were included in the matchday 22 for the historic success in Cape Town, with John Bentley's hat-trick heroics earning him a start in the second Test. Neil Jenkins played 40 minutes and scored one of seven tries in between kicking the Lions to glory on the big stage, while Neil Back, Eric Miller and Austin Healy all made the Test bench after starting against Free State.
"Your mid-week team's attitude and intensity makes the series - we've said that right from the outset," said Rowntree.
"On Saturday they were the ones straight into the changing room after the game congratulating the lads and they're the guys who had to get up on Sunday morning and train. We were very careful about how we picked the squad with that in mind. Their attitude has been impeccable so far.
"Those guys have all been told they have a chance to make the Test squad. For the squad that takes the field tomorrow, there are a lot of opportunities there for guys to be involved at the weekend. I am sure there will be a handful of guys who take the field on Saturday who will play tomorrow."
The Lions' most-recent mid-week display also adds an extra spice to their first encounter with the Rebels, given that things didn't exactly go to plan against the Brumbies this time last week.
Rowntree saw his side beaten 14-12 in Canberra on June 18 as Britain and Ireland's elite tasted defeat for the first time in 2013. It was a result and a performance that didn't sit well with a proud group of players and coaches and Rowntree expects a similarly positive response to the one he witnessed at the Suncorp Stadium on Saturday.
"Very much, we want to finish with style. That didn't go down very well that loss. There were some stern words at half time and afterwards as well," added Rowntree, who is delighted that the Lions will face another stiff challenge after the Rebels named their strongest possible side.
"A lot of the guys playing on Tuesday night were involved in that and this is their chance to right those wrongs. I thought the Brumbies were exceptional. They were a very well drilled team, they gave us a real challenge and I think the breakdown challenge in that game set us up well for the weekend.
"If the Rebels have seen how the Brumbies played last week, they'll know where they want to get into us, so to speak. It's a familiar looking team to what we've been looking at in analysis. There are some familiar faces there.
"For a lot of those guys, it would be a major milestone in their careers if they were to beat the British & Irish Lions, just like it was for those Brumbies players last week. It will be a fierce hit out, which is just what we need at the moment."