Third in the Zurich Premiership, they ensured all four top sides in the league ended with a trophy, while victory also gave them the second seeding for English clubs in next year's Heineken Cup.

With Gloucester leading 22-13 with eight minutes left, Johnstone's try, converted by fly-half Felipe Contepomi, saw Bristol close to within two points.

But a second needless penalty conceded by former England lock Garath Archer allowed Mercier to relieve the pressure with his sixth penalty.

And despite Contepomi maintaining his 100% kicking record to again narrow the gap to two points, Mercier's final penalty three minutes into injury-time brought relief to Gloucester.

They led 16-6 at half-time after asserting themselves with the game's opening try six minutes before the interval.

The Frenchman had earlier given his side a 6-0 lead with two penalties in a scrappy opening quarter, before Contepomi replied with two of his own.

Bristol wing Phil Christophers joined Collazo in the sin-bin after 26 minutes for cynically holding back Tom Beim.

But both sides struggled for forward momentum as Gloucester's centre pairing of Terry Fanolua and Robert Todd thwarted Bristol's best attacks with a series of crunching tackles.

Fanolua came closest to a second Gloucester try just before the hour when he was held up over the line by a superb tackle from Bristol flanker Michael Lipman.