O'Halloran's 75th-minute effort was too little too late as Rovers fell to a 2-1 defeat to Leyton Orient at Brisbane Road on Saturday, with the O's goals coming from Charlie MacDonald and Martin Rowlands, the latter also missing a penalty.
Second-placed Doncaster failed to take advantage as they sunk to a shock 2-1 home defeat against Walsall.
Andy Butler put the Saddlers in front with just two minutes on the clock and despite Billy Paynter's quick equaliser, Walsall still won it when Febien Brandy fired home nine minutes from time.
And third-placed Swindon were left embarrassed by a 1-1 home draw with bottom club Hartlepool.
Simon Ferry gave Swindon a 15th-minute lead but Andy Monkhouse's 74th-minute equaliser means Hartlepool have now gone three games without defeat.
Bournemouth were the ones to take advantage as they moved to within one point of an automatic promotion place by heaping more misery on south coast rivals Portsmouth.
Second half goals from Lewis Grabban and Marc Pugh secured a 2-0 win for the Cherries and made it a ninth straight defeat for Pompey, who were threatened with the threat of expulsion from the league last week.
Sheffield United also closed in the leaders with a 2-1 win at Shrewsbury. Michael Doyle and Dave Kitson gave the Blades the lead in the second half before Stephen McGinn's late consolation.
Yeovil beat play-off rivals Coventry 1-0 at the Ricoh Arena with Paddy Madden scoring the only goal of the game in first-half injury time.
But Brentford's play-off hopes were hit by a 2-2 home draw with lowly Bury.
Harry Forrester's opener was cancelled out by Tom Soares and although Marcello Trotta put the Bees back in front, Nicky Ajose salvaged a point for the visitors late on.
After sacking Paul Dickov in midweek and taking one point from a possible 27, Oldham finally got back to winning ways with a 3-1 victory over MK Dons under caretaker-boss Tony Philliskirk.
Lee Barnard's early strike was cancelled out by Daniel Powell but a Jean Yves Mvoto header restored the home side's advantage before Chris Iwelumo netted the Latics' third on 53.
Carlisle edged past Stevenage 2-1 at Brunton Park after the visitors had keeper Steve Arnold sent off with just 12 minutes gone.
Rory Loy had put the Cumbrians in front after nine minutes before Arnold saw red for a foul on Loy.
Lee Miller scored the resulting penalty to make it 2-0 then Marcus Haber reduced the deficit for the visitors.
Scunthorpe hit back to beat Crawley 2-1 at Glanford Park. Matthew Sparrow put the visitors in front after 48 but goals from Jimmy Ryan and Niall Canavan earned the points.
Luke Murphy's penalty was cancelled out by John Cofie as Notts County came back to earn a 1-1 home draw with Crewe, while Freddie Sears struck the only goal for Colchester against Preston, who had Bailey Wright sent off late on.