Carroll struck 10 minutes into either half to take his tally for the season to 14, a figure Lovenkrands had reached earlier with his 22nd-minute effort, as relegation-threatened Scunthorpe wilted in the face of an onslaught at St James' Park.
The game might have been over by half-time but for Iron goalkeeper Joe Murphy, the crossbar and the offside flag which denied Kevin Nolan a 12th-minute header.
But the Magpies did more than enough to re-establish their four-point advantage over second-placed West Brom and leave themselves needing a maximum of 15 points from their remaining 10 games to clinch promotion.
Scunthorpe arrived on Tyneside as only one of four sides to beat Newcastle in the Championship this season, and that reverse on October 20 appeared to galvanise Chris Hughton's men, who had lost just one of the 22 league games they had contested since.
The Magpies, who had scored 18 goals in their previous four home games, went in front with 10 minutes gone when Carroll met Danny Guthrie's corner with a thumping header to claim his 13th goal of the season.
Nolan had the ball in the net once again two minutes later when he headed home Guthrie's rehearsed free-kick, only to see his effort ruled out for offside.
The Iron escaped once again with 16 minutes gone when Lovenkrands smashed the ball against the crossbar after Murphy had spilled Jose Enrique's cross, but the goalkeeper redeemed himself with a fine save from Carroll's powerfully-struck shot three minutes later.
However, Murphy was left cruelly exposed once again with 22 minutes gone when Wayne Routledge's defence-splitting pass put Lovenkrands in on goal and the Dane finished superbly to make it 2-0.
The goalkeeper pulled off a stunning point-blank stop to deny Lovenkrands a second five minutes later, and his goal continued to lead a charmed life as Scunthorpe somehow managed to get the to break without conceding again.
But Newcastle increased their lead in fine style with 55 minutes gone.
Fabricio Coloccini picked up possession deep inside his own half and fed Guthrie, whose ball over the top allowed Carroll to race away and chip a delicate shot over the advancing Murphy.
Steve Harper had to make a good save from Jonathan Forte seconds later and another from substitute Martyn Woolford with nine minutes remaining, and in the meantime Jonas Gutierrez had seen a 71st-minute strike disallowed for offside.
Murphy palmed away a well-struck effort from Gutierrez after and enterprising 87th-minute run from halfway, but the damage had been done long before.