Ireland coaches Andy Farrell, Greg Feek and Richie Murphy were on hand to witness the return to play of Cian Healy and Rob Kearney.
Leinster coach Leo Cullen would have been just as eager to see how his half-backs Jamison Gibson-Park and Joey Carbery combined.
First, he would have to suffer through the leak of 13 points in 14 minutes. Bath looked the business right form the off, getting their big men on the ball for Toby Faletau and Matt Garvey to create the space for Rhys Priestland to open up with three points.
It would take the right, in-season attitude for Leinster to make their mark.
Garvey was involved again before Dave Attwood steamed over at the end of a breathtaking counter-attack, Priestland taking them 10 clear. The Leinster scrum was demolished, their fringe defenders driven back in contact from a sound lineout, concluding in a Priestland penalty.
The first glimpses of class from Gibson-Park and Kearney, from sure handling, put Adam Byrne in for a sweet try. Then, Healy burst upfield and Garry Ringrose's footwork added yards for Ross Molony to take advantage of hooker Ross Batty's poor positioning for a second try in two minutes, Joey Carbery's extras making it a one-point game.
Wing Byrne went close down the left and James Tracy was held up over the line as the home side pressed for the lead. Anthony Watson was not as generous, his handywork opening the space for Jeff Williams to make the right corner for Priestland to add two.
It took the intervention of Dan Leavy to quiet another dangerous move before a Rory O'Loughlin half-break prompted a response in which Peadar Timmins came within inches of a touchdown. At half-time it was 12-20.
The 10 Leinster half-time replacements and the four which quickly followed in the first five minutes of the second period did nothing for their cohesion.
Bath calmly exposed the chinks in Leinster's armour when Samesa Rokodoguni got over in the 64th minute.
Leinster were moving with menace when Rokodoguni slapped down the ball to see yellow.
It was no coincidence Leinster's Zane Kirchner came calling down the left for Barry Daly to put Rory O'Loughlin in. Ross Byrne's conversion narrowed it to six points (19-25).
This was countered by a classy move from Harry Davies as he collected his own kick to score. In the last minute, an interception by George Ford put the game to bed as the visitors scored 14 point in the last five minutes.