Three second-half goals saw Orient claim only their second home win of the season at a busy Brisbane Road on Saturday.
A crowd of almost 7,000 braved a grey and wet day to see Joe Widdowson, Matt Harrold and Conor Wilkinson cancel out Stuart Sinclair's first-half opener for the Saddlers.
And the only negative for Ross Embleton's side was a late red card shown to Wilkinson, for an off-the-ball clash with Dan Scarr, as O's climbed above their rivals into a mid-table position.
The hosts created the first notable chance on six minutes as Dale Gorman threaded a ball into the path of James Brophy on the left and he got to the byline and saw his cross hit a defender and loop up, but referee Ben Toner awarded Walsall a free-kick as Wilkinson challenged goalkeeper Liam Roberts.
The visitors went close on 10 minutes, though, when from one of many attacks on the left, a deflected cross had Dean Brill scrambling to his near post to keep the ball out.
Good footwork by Gorman earned O's a free-kick on the right corner of the box on the quarter-hour mark and Josh Wright's low effort found the side netting, before Wilkinson's low cross from the right was just behind the midfielder.
Dan Happe had a header from a Wright corner hooked away by a Walsall defender, before Wilkinson's low drive forced a save from Roberts.
But just as O's were building momentum, they fell behind on 20 minutes when a low cross from the left was not sufficiently dealt with by Dean Brill and Stuart Sinclair scrambled the loose ball home from six yards.
Myles Judd blocked a shot from the dangerous Wesley McDonald soon after, while Harrold had the ball in the net at the other end but was flagged offside.
But Walsall looked the more threatening side going forward and Dan Scarr dragged a shot wide from the edge of the box after being teed up by the tricky Anderson.
Wilkinson saw a header from Jupp's cross drop harmlessly over the crossbar, then had a shot blocked in the box following some patient build-up play through midfield, where Craig Clay, Wright and Gorman were dovetailing nicely.
Brill smothered a header from Zak Jules on 39 minutes, while Happe cut out Rory Holden's left-wing cross as Walsall countered just before the break.
And Brill had to field a low shot from Holden in the opening minute of the second half as the visitors began brightly in the persistent rain.
But O's were back on terms on 48 minutes when a promising move looked to have broken down, only for the ball to reach left-back Widdowson, who arrowed a right-footed shot into the far corner of the net to level in stunning style.
Walsall were soon back on the ball, looking to restore their lead, but Happe had a header from Gorman's free-kick pushed around a post by Roberts and was then booked for blocking the keeper's attempts to throw the ball out having claimed the corner.
And the hosts took the lead just past the hour mark when a slip by a Walsall defender allowed Clay to advance into the box on the right and unselfishly square the ball for Harrold to sweep inside the far post.
The tireless Gorman made way for George Marsh midway through the second half, with Wright clipping a shot from Wilkinson's pass over the crossbar soon after.
And Orient went 3-1 up with 15 minutes remaining when Harrold headed on a long ball from the back, Brophy chested it into the path of Wilkinson and the striker cut inside before sending a left-footed shot past the wrong-footed Roberts.
Wilkinson went from hero to villain on 80 minutes, though, as he clashed with Scarr by the touchline and was given his marching orders, while the Walsall defender was shown a yellow card for his part in the incident.
The 10 men held firm in the closing stages, as Walsall substitute Elijah Adebayo missed a gilt-edged chance at the far post and a string of decisions by Toner were greeted with boos by the home faithful.
Orient: Brill, Widdowson, Gorman (Marsh 67), Coulson, Clay, Wilkinson, Judd, Happe, Brophy (Dayton 90), Harrold (Alabi 83), Wright.
Unused subs: Sargeant, Maguire-Drew, Dennis, Ogie.
Walsall: Roberts, Clarke, Scarr, Sinclair, Kinsella, Holden (Adebayo 67), Guthrie (Norman 63), McDonald (Gordon 67), Liddle, Gaffney, Jules.
Unused subs: Rose, Sadler, Hardy, Bates.
Attendance: 6,951 (including 852 Walsall fans).
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