Martin Rowlands's second minute strike was enough for Ian Holloway's men to see off The Robins and should Bristol City lose at Barnsley on Sunday, they will be heading back to Division One with champions Plymouth Argyle.
Swindon are not assured of a play-off place following the defeat and will need a result on the last day of the season to earn post-season football.
Champions Plymouth celebrated their promotion with a final away victory by defeating play-off hopefuls Hartlepool United 3-1 at Victoria Park.
Pools took the lead through Adam Boyd after 11 minutes, but the visitors were level a minute later through Lee Hodges.
Nathan Lowndes made it 2-1 three minutes before the break before Mark Tinkler put into his own net three minutes after half time.
Hartlepool still need a result on the final day of the season to assure a play-off place.
Brighton & Hove Albion have reached the play-offs following a 1-0 win over relegated Notts County at The Withdean Stadium.
A Kelvin Wilson own goal with 16 minutes left gave The Seagulls a ticket into post-season football later this month.
Port Vale kept their hopes of reaching the play-offs alive with a last-gasp 2-1 win over an improved Tranmere Rovers at Vale Park.
Stephen McPhee put Vale in front after 10 minutes but Paul Hall equalised midway through the opening half for Rovers.
In the dying moments, McPhee got his second goal to delight the home crowd and take the play-off race to the last day of the season.
Stockport County have secured their Second Division status with a 0-0 away draw at Bournemouth.
Luton Town heaped more misery on Sheffield Wednesday after a last-gasp 3-2 win at Kenilworth Road.
Jon Shaw had put The Owls in front on 23 minutes before Terry Cooke gave the visitors a second goal ten minutes later.
But in the second half, The Hatters got back to level terms with goals from Steve Howard (54) and Steven O'Leary (78).
In the dying moments, Howard pounced again to secure the three points for Mike Newell's side.
Rushden & Diamonds are in the relegation places following a 2-0 defeat at Colchester United.
The visitors went a man short when Barry Hunter was sent off for a second bookable offence on 73 minutes.
In the last nine minutes, The U's secured the win with a Scott McGleish penalty and a late Gavin Johnson strike.
Wrexham were held to a 1-1 draw by relegated Wycombe Wanderers at The Causeway Stadium.
Roger Johnson gave The Chairboys the lead on 79 minutes before Chris Llewellyn equalised a minute later for a share of the spoils.
Peterborough United have nearly secured their place in Division Two after thrashing Blackpool 4-1 at Bloomfield Road.
Curtis Woodhouse put The Posh in front with a penalty on 19 minutes before scoring again seven minutes later.
Martin Bullock replied for The Seasiders soon after going 2-0 down, but second half strikes from Calum Willock (53) and David Farrell (58) gave Barry Fry's side a huge away win.
Grimsby Town pulled out of the bottom four with a vital 1-0 victory over Brentford at Blundell Park.
Isaiah Rankin's 70th minute strike was enough to take The Mariners two points clear of the drop zone, with one match left in the season.
Finally, Chesterfield face needing a win to have any chance of staying up after going down to a 2-0 defeat at Oldham Athletic.
A second half brace from John Eyre was enough to give Brian Talbot's side all three points at Boundary Park, with The Spireites two points adrift of safety going into the last week of the season.
Click below for match summaries:
Division Two
Blackpool 1-4 Peterborough
Bournemouth 0-0 Stockport
Brighton 1-0 Notts County
Colchester 2-0 Rushden & D'monds
Grimsby 1-0 Brentford
Hartlepool 1-3 Plymouth
Luton 3-2 Sheff Wed
Oldham 2-0 Chesterfield
Port Vale 2-1 Tranmere
QPR 1-0 Swindon
Wycombe 1-1 Wrexham
Click here for an updated Division Two table.
