The hosts were handed an early lead by Scott McDonald but never managed to assert their authority as Keane's men fought back with their quickfire double before Jon Stead added a third late on.
Millwall celebrated their return to the Championship by subjecting David James to a torrid afternoon in a 3-0 victory over Bristol City at Ashton Gate.
The England goalkeeper was beaten by Darren Ward and Danny Schofield either side of half-time before Paul Robinson put the Lions in dreamland on the hour mark.
However, there was a sour note to Millwall's day as Darren Carter was sent off for two bookable offences.
The Scotland international, a summer signing from Wolves, headed home on the stroke of half-time to ensure a winning start for Brian Laws' men.
Bostock, signed on the eve of the campaign on a loan from Tottenham, laid the foundations for victory by rattling home a stunning 30-yard strike to help Nigel Pearson mark his first game in charge with a win.
Returning captain Ian Ashbee made the points safe in the 49th minute, punishing Dorus De Vries' error.
Last season's play-off semi-finalists were put to the sword in the first half at Selhurst Park thanks to goals from Wilfred Zaha, Darren Ambrose and Alan Lee.
Leicester dominated the second period and goals from Andy King and DJ Campbell saw them fall just short.
Icelandic forward Helguson, whose days in west London appeared to be numbered when he was farmed out to Watford last season, was ice-cool from the penalty spot in the first half and Hall, who spent the end of the campaign on loan at Newcastle, tapped in the fourth.
In between, former Plymouth forward Mackie opened his account with a predatory strike and Taarabt, who completed his permanent switch from Tottenham on Thursday, capped a sparkling display by tucking away the hosts' second spot-kick.
Cash-strapped Pompey, relegated from the Premier League in May after seven seasons in the top flight, were undone by a brace from Freddy Eastwood.
New-look Preston endured a bitterly disappointing 2-0 defeat at the hands of 10-man Doncaster.
Rovers established an early two-goal advantage with goals from James O'Connor and James Hayter to secure victory before the late dismissal of debutant midfielder Simon Gillett.
Garry Thompson's controversial goal helped Scunthorpe on their way to an impressive 2-1 win at Reading.
Thompson appeared to have been flagged offside as he gave the Irons an early lead, but the goal stood to the fury of Reading boss Brian McDermott.
Gylfi Sigurdsson drew the Royals level with a typically fine hit but giant centre-half Rob Jones was able to head in a second-half winner for the visitors.
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