But head coach Robbie Deans altered his stance on keeping all his Test players out of The Lions' warm up matches and presented Dennis with the option of getting an early look at the tourists a week out from the opening international in Brisbane.
"The chance to play and to lead my state in front of a full house, it's really special and it means a lot to me," said Dennis, who will start at No8 at the Allianz Stadium.
"I came back as soon as I could. He (Deans) said: 'If you had the opportunity to play on Saturday, would you?' I said 'yes'. That was it.
"I've never played in a full house in a Waratahs jersey. It's extremely important for us - to represent this state against such a strong international side, it's really special.
"None of us will get this chance again. We respect The Lions and know what it means to their group but it also means a lot to us."
Dennis' inclusion in the Waratahs line up has led to suggestions that he is now behind the eight ball when it comes to winning a Test place a week today but the man himself has a more positive take on the situation.
A strong showing against Warren Gatland's men would do his chances of securing a starting spot in his country's back row no harm at all - a point that has already been proven by Luke Morahan's squad call up almost immediately after his stunning solo display for the Reds in game three last Saturday.
"I'm still in the frame for (international) selection," added Dennis, who knows a first New South Wales win over The Lions since 1959 would be the best way to boost his Test ambitions.
"I'm still very much part of the Wallabies squad. I'll hopefully contribute throughout the whole series at some stage.
"I'm very much focused on (today) and, if the group goes well, I'm sure that will help with my selections down the path. It's a good opportunity to push myself a little bit, but I'm down here to win with the boys."
So how does Dennis intend to ensure a Waratahs win becomes a reality in The Lions' penultimate fixture before the first Test?
In short, he will be telling his troops to keep things simple, to do the basics well, take the tourists' on physically but legally, and to enjoy the occasion rather than be overawed by it.
"The boys are really excited about it. There's no fear and we'll just get stuck in.
"I want to beat those blokes and we won't beat them with 13 or 14 men. We need to be smart around that. There's good ways of hurting them but you have to make sure you do that legally rather than illegally.
''It's going to be a big challenge. With this game you can challenge any team you play but when it comes to individual roles around the set-piece, that's when you might see a few differences. I've got confidence in Paddy Ryan, Jeremy Tilse and John Ulugia. It's a great front row, and I've got confidence in the lineout with a few of the younger guys.
"We need to hold on to the ball and play how we've played all year, but we need to do that at another level, a higher intensity.
"They don't know what they're going to face until we get out there. Likewise we don't know what they're going to throw against us.
"We're just going to keep it simple, be physical and go at it. We're not going to get bogged down in the fact that they are The Lions and we are the poor old Waratahs. The reality is it's a two-horse race and we're going to try and knock them off."