Hermann Hreidarsson struck his first goal in over a year as Portsmouth served warning of a late play-off challenge in the npower Championship with their sixth successive league win, beating Sheffield United 1-0.
Iceland international Hreidarsson slammed the ball home from close range following David Cotterill's corner midway through the first half and helped marshal a Pompey defence that kept a sixth successive clean sheet.
But while Steve Cotterill's side climbed to within striking distance of the top six, Sheffield United appear to be in freefall under manager Micky Adams, who has yet to taste victory in 13 matches since taking over from Gary Speed as Blades boss in December.
The Blades, unchanged from the side that lost at Bramall Lane to Derby last week, were first to threaten when striker Ched Evans rifled a 25-yard shot over the crossbar in the 10th minute.
But with Pompey winger Cotterill looking to impress against his former club, the home side moved quickly through the gears and began to dominate possession.
Leading goalscorer David Nugent forced United goalkeeper Steve Simonsen into a fine save with a low shot from inside the penalty area, and Pompey defender Greg Halford, another former Blade, drilled a 35-yard free-kick over the crossbar before Portsmouth opened the scoring.
Cotterill swung over a corner in the 24th minute and after Nugent and Johnny Ertl's aerial challenge, the ball broke for Hreidarsson on the edge of the six-yard box and the Iceland international lashed it high into the roof of the net for his first goal since December 2009.
Portsmouth continued to look the more accomplished outfit, but save for Hreidarsson's thumping header that flew just wide in the 43rd minute, neither side created another clearcut chance before half-time.
Pompey striker Dave Kitson brought the best out of Simonsen again four minutes into the second period, driving in an angled shot from 12 yards that the visiting goalkeeper pushed away, while Nugent dragged a similar effort wide soon after.
Blades midfielder Stephen Quinn struck a shot from the edge of the penalty area wide in the 64th minute, but although the visitors enjoyed a more equal share of possession as the second half progressed, there was little precision in the final third.
Pompey midfielder Hayden Mullins threatened to add a second when he rifled a 20-yard shot over the crossbar, before the Blades threatened in a rare foray into the hosts' box, substitute Sam Vokes heading straight at home goalkeeper Jamie Ashdown.
Vokes went close again in the closing stages with another header, this time from Bjorn Helge Riise's cross, as the visitors mounted a desperate late rally to salvage a point, but Adams' side slipped to a third successive defeat and are now six points adrift of safety.
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