Collins scored a first-half hat-trick as the black, green and gold flew into a 24-3 lead by the break.
But the Falcons fought back, scoring twice to cut the gap to seven points before a late Alex Mitchell try not only made sure of a 31-17 win but a bonus-point, too.
It was the third away game in succession that Saints had won, dominating the first period before being pushed back after the break.
Chris Boyd's men now sit fourth in the Gallagher Premiership, above Harlequins on games won with two matches of the regular-season to play.
And Collins said: "The boys were buzzing in the first half and I don't really know what went wrong in the second half.
"We were almost perfect in the first half, which is what we strive to be throughout the week.
"We spoke at half-time about looking after the ball and scoring next but it didn't really work in our favour.
"It's something in our game we're going to have to work on because if we make top four and end up getting to semi-finals, in the second half we're going to have moments we need to take and we're going to have to look after the ball.
"Against the likes of Saracens, Exeter, Gloucester we're going to have to do those small details."
Saints' next game comes at home to Worcester Warriors on Saturday.
And Collins is desperate to give the Franklin's Gardens faithful something to shout about in the final home match of the season.
"This week's a tough one as well," said the speedy wing.
"It's our last home game and we want to go out with a bang in front of our home fans as well.
"We'll keep going.
"We want to get top four, it's where we're aiming and we'll try to get there."