(tries Short, Eadie, Hughes; con Jarvis; pen Robinson)
London Welsh 21
(tries Vella, Stegmann; con Ross; pens Ross 2; drop goal Ross)
London Welsh win 48-28 on aggregate
A smash and grab raid saw London Welsh pip Bristol on the night and secure promotion to the Premiership by a 20-point margin.
Trailing by 19 points before kick-off, the hosts had reduced that deficit to eight with ten minutes to go.
Although Bristol dominated their final match at the Memorial Stadium, late tries from Nathan Vella and Seb Stegmann not only gave Welsh an immediate top-flight return, but denied the hosts a consolation victory.
It could have been different had Bristol fly half Nicky Robinson kicked better off the tee, but this was another battling display from Justin Burnell's warriors.
Ultimately, the damage had been done with Welsh's 27-8 victory at Oxford's Kassam Stadium in the first leg, but this was the icing on the cake.
Bristol began full of intensity, but Welsh managed to secure a clearing penalty.
The opening scrum on five minutes yielded Bristol a penalty and a kick to the corner.
From here, the visiting defence conceded a further penalty inside the 22, but Robinson's eighth minute kick squirted wide.
Robinson saw a further long-range attempt miss the left upright on 12 minutes.
Bristol continued to have most of the play without creating scoring chances.
Welsh fly half Gordon Ross was happy to kick the ball in the wet conditions and his side were pleased to reach the quarter mark scoreless.
The visitors' first foray into the Bristol 22 produced the opening points.
Several pick and drives set up a successful drop goal attempt from Ross on 28 minutes.
London Welsh's Mitch Lees claims line-out ball
Bristol's progress was hamstrung by several knock-ons, while Welsh showed good enterprise to run the ball clear through wing Stegmann.
The hosts looked to have wasted a good chance when they lost a close-range line-out, but scored the opening try soon afterwards.
Robinson's cross kick picked out wing Andy Short, who did well to get over the line, with the video referee confirming the score amid appeals the ball was held up.
Welsh lost full back Alan Awcock to injury, but replied soon afterwards with a penalty from Ross via a post.
Visiting scrum half Chris Cook was sin-binned for a deliberate knock-on as the hosts threatened again.
Bristol ended the half 8-6 ahead on the night when Robinson slotted a penalty on the whistle.
The second half had barely started when Bristol worked an excellent line-out move and No 8 Mitch Eadie powered over in the corner.
Robinson's conversion went wide, but Bristol were 13-6 ahead and trailed by just 12 on aggregate.
The hosts continued to press as the atmosphere ratcheted up even further.
Robinson, however, was struggling with the boot and sliced another penalty wide.
Ross, however, was in better form and made it 13-9 with a 68th minute penalty.
Bristol were not rolling over and Adam Hughes barged through for a try, converted by fellow replacement Adrian Javis.
That reduced the arrears to eight points and the hosts had real hope.
London Welsh's Gordon Ross kicks for position
But just as they had against Leeds at the Kassam Stadium, Welsh finished with an astonishing burst to win the second leg.
A superb driving maul saw replacement hooker Nathan Vella power over in the corner, with the try awarded after a lengthy visit to the TMO.
That ended any hopes of Bristol gaining promotion, but having dominated for so long, they didn't even have the consolation of a home win.
This was because Stegmann hacked a loose ball through from halfway to outpace the defence and ground it by the posts.
Ross's conversion incredibly put Welsh 21-20 up on the night.
Bristol pushed for a fourth try, but the visitors won a penalty to clear and end an incredible game.
Bristol: Wallace, Amesbury, Tovey (Hughes 68), Mosses, Short, Robinson (Jarvis 57), Tipuna (capt) (Grindal 76), Traynor (Hall 61), Johnston (Laurence 61), Cortes (Hobson 57), Glynn, Townson, Koster (Skirving 69), Mama, Eadie.
London Welsh: Awcock (Crane 35), Stegmann, May (capt), Jewell, Scott, Ross, Cook, Trevett (Bristow 50), Morris (Vella 60), Edwards (Tideswell 41), Spencer (West 54), Corker, Lees (Stedman 68), Kirwan, Thorpe. Rep not used: R Lewis.
Referee: L Pearce (RFU).