Tries from Nick Burrows and Declan Danaher had looked like sealing the match for the Exiles, who had the trusty boot of fly-half Barry Everitt to thank for 20 of their points with six penalties and two conversions.
Bristol however managed four tries on the day for a bonus point to add to their two points for drawing, Brendan Daniel’s early effort as well as a first half penalty try being added to by Australian Shane Drahm before Nelson’s dramatic late score.
Drahm added three conversions and two penalties for the Shoguns, but could not apply the finishing touch for victory with the late conversion, regular kicker Felipe Contepomi being away on international duty with the Argentine Pumas in Italy.
Bristol ShogunsTries: Daniel, Penalty try, Drahm, NelsonCons: Drahm 3Pens: Drahm 2
London IrishTries: Danaher, BurrowsCons: Everitt 2Pens: Everitt 6