Orient were so close to a first home win of the campaign against Carlisle, but were denied by a stoppage-time equaliser.
Carlisle captain Paul Thirwell levelled to make it 2-2 in the 92nd minute.
Earlier, Scott McGleish had brought the O's to the cusp of victory with two second half goals to rule out Matt Robson's first half opener.
Luke Ashworth started in defence in place of Ben Chorley.
Sean Thornton was missing with a knee problem.
Glenn Morris got his first start of the season with Jamie Jones ruled out with a hip injury.
A thin crowd at Brisbane Road had little to cheer about during the first half.
Orient struggled to turn possession into penetration, and Carlisle always looked the most likely to break the deadlock.
On 10 minutes, after a quiet start to the game, Carlisle Utd fired off the first shot of the game when Joe Anyinsah shot at Morris after cutting into the box having beating Ashworth for pace.
Orient looked to Andros Townsend for attacking threat, firing long balls towards him out on the left wing.
On 13 minutes, Anyisah headed wide from point-blank range at the near post after Ashworth's clearing header had returned the ball right back to where a previous cross had just come from.
The quiet Orient crowd was first roused on 17 minutes when Scott McGleish, who started up front with RYan Jarvis, made to meet with an overhead kick JJ Melligan's cross from the right.
The effort was amibitious but no repeat of his strike against Newcastle, last month.
On 32 minutes, Smith struck a loose ball over the bar after a rare period of sustained Orient pressure in the final third.
Carlisle went ahead on 41 minutes with a swift break from inside their own half. Matt Robson finished off Tom Taiwo's through ball with a low shot past Morris into the far corner.
The goal came straight from Orient's best phase of play. Townsend had left his marker on the floor, then Jarvis had persisted at the edge of the box to spray the ball to Melligan on the wing.
His cross was met by McGleish who nodded just over the bar.
The second period saw a role revesal. Carlisle never got going and Orient went firmly onto the front foot.
Orient's reponse in the second half was instant.
A minute in, McGleish levelled with a re-taken penalty, after Peter Murphy was ajudged to have gone in with a high boot on Jarvis while the pair battled over Jason Demetriou's cross.
Chambers replaced Townsend on 53 minutes.
Five minutes later, Morris was at full stretch to palm away Anyinsah's header. He saved at point-blank range soon afterwards.
The game simmered and boiled over. Luke Ashworth got booked on 64 minutes for unsporting behaviour.
Almost straight afterwards, Paul Thirwell was booked when he went straight through Melligan.
Boss Geraint Williams replaced Jarvis with Adrian Patulea on 68 minutes to add bite up front.
He was to be rewarded for it.
Scott McGleish rifled a 20 yard effort just past the post after Chambers'had battle to distribute possession in Carlise's final third.
The final ten minutes provided as much excitement as the entire match beforehand.
He fired Orient ahead on 84 minutes thanks to a delicious piece of link up play with Patulea.
The Romanian turned his marker and laid the ball in front of McGleish 12 yards out. The veteran kept cool to lift a chip over Lenny Pidgeley.
He almost had a hat-trick two minutes later but Pidgeley blocked his shot.
Morris made himself a hero on 91 minutes with a Gordon Banks 1970-esque one-handed save from Gary Madine's header.
But Orient's home curse struck via the boot of Thirwell. In extra time he bent a shot into the far corner.
Orient so deserved a first home win of the season, but for now the wait continues.
Attendance: 3,546
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