The Brazilian attacker struck twice in four second-half minutes at the Estadio da Luz to propel Jorge Jesus' quadruple-chasers seven points clear with just two rounds remaining
The Estadio da Luz was growing increasingly restless as the Eagles struggled to break down their stubborn opponents - despite dominating both possession and territory.
However, Lima broke Olhanense's resistance just before the hour-mark and struck again just four minutes late to seal Benfica's 33rd Primeira Liga title.
The Eagles had gone into the weekend seven points clear of second-placed Sporting, who cut the gap with a win over Belenenses on Saturday night.
That left Jorge Jesus' men knowing that nothing other than victory against Olhanense would clinch the title with two rounds remaining.
Consequently, the Benfica boss ignored the temptation to rest some star men ahead of Thursday's Europa League semi-final first-leg clash with Juventus and named a strong starting line-up.
He was perhaps made to regret that decision, though, after Toto Salvio was forced off with an apparently serious arm injury, with Lazar Markovic coming on in the in-form winger's place for the start of the second half.
Benfica became increasingly desperate the longer the game wore on but their incessant pressure finally told in the 57th minute when Lima netted.
The pressure lifted, and Olhanense's resistance belatedly broken, Lima struck again moments later to send the home fans wild and keep Benfica on course for a remarkable quadruple, with Juve to come in the Europa League, and final dates already booked for both the Taca de Portugal and Taca da Liga.