The striker headed home from Merouane Zemmama`s cross to help his side move seven points clear of the npower Championship drop zone.
In an entertaining match, the hosts drew first blood when Neil Harris, on his return to the starting line-up, coolly finished after collecting from Steve Morison`s flick-on.
The Lions had several chances to extend their lead but they were pegged back by Tony McMahon`s fantastic free-kick and they then fell behind thanks to Scott McDonald`s strike.
Hameur Bouazza came off the bench to score on his debut with a free-kick of his own before Lita ensured Boro`s first win at Millwall since 1973.
The result is a blow to Millwall`s play-off hopes as they would have been hoping to close the eight-point gap on sixth-placed Leeds.
Source: PA
Source: PA