Shelvey, wearing the captain's armband for the Magpies, was dismissed shortly after half-time at St James' Park for petulantly treading on Alli.
It proved a crucial moment in a physical encounter as goals from Alli and Ben Davies helped Spurs earn three points in their Premier League opener.
Alli's conduct on the pitch has been called into question at times and he was banned for three matches after aiming a punch at West Brom's Claudio Yacob in April.
But the England midfielder told Sky Sports it was important for him and the team to keep a cool head.
"I've had a few talks with the gaffer [Mauricio Pochettino] and a couple of people," Alli said. "I've been caught out a couple of times with my temper.
"It's something I like to keep in my game and it was a game today when we had to keep our cool. There was no need to react today.
"We didn't want to get too heated up and get pulled into what they wanted us to and make it more of a physical battle than a game of football."
Newcastle had been competitive at St James' Park but, after Shelvey's dismissal, Alli tucked away Christian Eriksen's excellent cross to break the deadlock before Davies finished off a fine team move.
"We knew it was going to be a physical game today," Alli added. "They didn't make it easy for us and it’s a difficult place to come.
"We knew if we stuck to the game plan then the chances would come. They did and we put them away.
"[Shelvey's red card] happens sometimes in football. He's a great player and I'm sure he's going to be disappointed.
"It was important that we stayed professional and just did what we knew we had to do. We kept the ball moving, which was difficult at times, but I don't want to talk about it too much."