United's record £4million signing grabbed a goal in each half to take his tally to 11 and sink Jim Magilton's high-fliers.
The Suffolk side, who were chasing their first away win of the season, caught out United's sloppy defence twice in quick succession early on with a Jon Walters and Alan Lee combination.
The Ipswich midfielder found space on the right flank to pick out the big striker who turned quickly to drill in a low shot, saved at the foot of the near post by Ian Bennett.
Then Walters pumped over a low cross with Lee just failing to connect as he slid into the goalmouth.
United were in trouble again when they failed to pick up the striker as he ran onto David Wright's measured pass, but his shot from 14 yards rolled inches wide of the target.
The Sheffield side, with just one win from nine league games, squandered a half chance on 24 minutes when Danny Webber picked out David Carney and the Australia international crossed to Beattie, who finished with a tame header which was snapped up by Neil Alexander.
United finally snapped into life when Phil Bardsley fired a long-range free-kick narrowly wide, before Jason De Vos ended Webber's darting run into the box with a perfectly timed tackle.
The breakthrough came in the 33rd minute when midfielder Chris Armstrong threaded the ball to Beattie, who picked his spot from 12 yards and coolly planted the ball into the far corner.
Beattie almost had a second three minutes before the break as he jumped to meet a Webber cross, but the big man had to stretch and powered his header over the top.
Dangerman Beattie headed a Gary Naysmith cross narrowly wide before Walters levelled matters in the 54th minute by cheekily lobbing the advancing Bennett after chasing a long ball up field.
United were denied a penalty when Keith Gillespie was hauled down by Dan Harding, before referee Graham Laws finally pointed to the spot in the 71st minute after Liam Trotter had fouled midfielder Nick Montgomery and Beattie slammed the ball past the helpless Alexander.
Gillespie had the last word with a stunning right-foot drive into the top corner four minutes from time.