Fahad Al Muwallad scored for the second successive game for Juan Antonio Pizzi’s impressive side, which had brushed aside 10-man North Korea 4-0 in its opener at this year’s tournament.
A beneficial break off a Lebanon defender teed up Fawad to smash home the loose ball with his right foot, the ball flashing beyond goalkeeper Mehdi Khalil before he had time to react.
Saudi Arabia doubled its lead in the 67th minute, Hussain Almoqahwi poking home from close range, as it recorded back-to-back victories at an Asian Cup for the first time since 1996 - the year they last went on to be crowned champion.
Lebanon will regret its failure to take opportunities when only a goal behind, Joan Oumari wasting the best of them when he planted a free header from a corner wide of the target.
George Felix Melki also failed to make contact with a free-kick from deep when at full stretch, letting Saudi Arabia off the hook again towards the end of an open first half.
Lebanon remained in contention after the break thanks to their goalkeeper, with Khalil spectacularly denying Hatan Bahbri’s long-range strike before showing his bravery to rush out and deny Fawad.
However, Almoqahwi converted Bahbri’s teasing left-footed delivery from Saudi Arabia’s right flank to wrap up the points.
The three-time winner concludes its group fixtures with a clash against Qatar, which first takes on North Korea, in what could be a head-to-head battle to finish top of the table.