The bustling Belgian climbed highest in the Reading box to nod the ball home in the 80th minute, giving his struggling side a 1-0 win at Villa Park and lifting them clear of the Premier League relegation zone.
Aston Villa have found goals hard to come by this season under new coach Lambert and before Tuesday's game had scored just 10 in 13 games - the joint fewest in the league.
Leaving out the club's record signing Bent, who cost £18m last year, was a controversial decision by Lambert but the Scot was delighted with 21-year-old Benteke's impact.
"He's been fantastic for this club and for the national team. And he's getting better," Lambert told Villa's official website. "He's only 21. He might not hit his peak till his late 20s.
"He does get chances too in matches. He always does - whether it be headers or shots. He's been great."
In a match of few chances, Villa's Brett Holman struck a crisp shot centimetres wide early in the second half and Adam Le Fondre should have put Reading ahead when he sent a free header wastefully over the bar.
The deadlock was broken 10 minutes from time when Benteke rose at the far post to head Ashley Westwood's corner firmly into the far corner of the net.
Lambert lauded his side's composure against Reading and said the win, which moved them up to 17th in the 20-team league, could be crucial in the fight to survive.
"You have to keep your nerve. They did that," he added. "I thought it was just a big result. I knew this would be a tough game. But this is what happens in this league. It's a big win."
The defeat for Reading leaves the newly-promoted side mired in the relegation battle. The Royals are second from bottom on nine points, four adrift of Villa.
