Debutant Scott Laird volleyed agonisingly wide, but Revell's 78th-minute spot-kick sealed all three points for the Cobblers, who are now unbeaten in 31 league matches.
Jon Whitney made three changes to his Saddlers team. Scunthorpe loanee Laird came in, while Bakayoko and Maz Kouhyar were handed their first league starts.
Simeon Jackson and Andreas Makris dropped to the bench, as Isaiah Osbourne missed out through injury.
Northampton, undefeated in their previous 30 league fixtures, could have taken the lead after 40 seconds but Kenji Gorre blazed horribly over from inside the box.
Bakayoko, the Saddlers’ hat-trick hero against Grimsby in the Checkatrade Trophy last time out, caused the Cobblers’ rearguard real problems in the opening exchanges.
On 13 minutes, he took down Laird’s clipped ball and sent a rasping half-volley over the bar.
The young frontman threatened again moments later, as he outmuscled Brendan Moloney out wide, advanced into the area and tested Adam Smith with a low angled strike.
Shortly after, Bakayoko was in the thick of the action once more, as he teed up Erhun Oztumer to fire over from 20 yards.
Walsall had made the more assured start, yet it was Northampton who took the lead, against the run of play, on 23 minutes.
Harry Beautyman received possession out on the left and delivered an inviting cross into the middle which the unmarked Matt Taylor headed into the far corner.
Rob Page’s direct team then enjoyed a good spell, with Moloney cutting the ball back for Kenji Gorre but he shot too close to Etheridge.
The Saddlers almost drew level on the stroke of half-time, when Oztumer lifted an exquisite, inventive pass over the home defence to Laird, who fired a side-foot volley agonisingly wide of the far post.
Half-time: Northampton 1-0 Walsall
Northampton started the second half strongly and almost made it 2-0 on 49 minutes, but Etheridge made a super reflex stop to parry Revell’s towering header from Anderson’s centre.
The visitors were indebted to Etheridge again as he got down smartly to keep out Taylor’s 30-yard free-kick, as the Cobblers pressed for a second.
With Walsall struggling to make any headway going forward, Whitney shuffled his pack, bringing on Franck Moussa and Jackson for Kouhyar and Liam Kinsella.
But Northampton remained the greater threat, with Etheridge producing an excellent finger-tip save to flick over Revell’s powerful right-footed drive.
And the Cobblers sealed the win 12 minutes from time, as Revell made it 2-0 with a coolly-taken penalty after Jason McCarthy was penalised for handball.
Joe Edwards fired over and then tested Smith in stoppage-time with a well-struck 25-yard effort, but Northampton comfortably saw the game out.
Full-time: Northampton 2-0 Walsall
Team: Etheridge, Edwards, McCarthy, Toner, Laird, Chambers, Kinsella (Jackson 66’), Morris (Makris 80’), Oztumer, Kouhyar (Moussa 57’), Bakayoko.
Subs not used: MacGillivray, Dobson, Preston, Sangha.
Attendance: 5,538 (601 Walsall supporters).