He joined Portsmouth in the summer from Everton and Royle moved quickly this week to link up again with the big centre-back as he snapped him up in a loan deal until the end of the season.
United, hammered 5-1 at Portman Road in November, desperately needed a victory to give them an outside chance of automatic promotion after successive defeats against Brighton and Sunderland.
And the Bramall Lane side carved out the early chances against an Ipswich team which has leaked 24 goals away from home.
Danny Cadamarteri ran on to a Michael Tonge pass in the ninth minute but, with co-striker Andy Gray unmarked alongside, he tried his luck from 15 yards and his low shot was blocked by Jason De Vos.
Gray was foiled by Kelvin Davis two minutes later after Tonge's low strike was deflected. The ball fell nicely for the United striker whose shot on the volley was palmed round the far post by the Ipswich keeper.
The visitors responded in devastating fashion in the 20th minute as Unsworth cut inside from the left flank and slammed the ball into the roof of the net from the tightest of angles.
United should have equalised minutes before the interval when full back Leigh Bromby steered a stooping header wide of the far post as he stretched to meet Tonge's curling free-kick.
The Sheffield side tore into Everton from the restart with Gray threading his way through a packed defence before unleashing a low strike which produced a spectacular one handed save from Davis.
Ipswich snatched a second against the run of play in the 61st minute. The ball was cleared to Ian Westlake whose fierce shot took a deflection and Shefki Kuqi finished off from close range for his 14th of the season.