Relegation-threatened Bristol City scored twice in the first 11 minutes as former leaders Leyton Orient slumped to a third successive defeat.
The visitors took the lead when Sam Baldock beat O's goalkeeper Shwan Jalal at his near post after three minutes.
Eight minutes later Tyrone Barnett was left unmarked to head powerfully home.
Kevin Lisbie pulled a goal back shortly before half-time, but Jamal was again at fault when defender Aden Flint headed in City's third.
VIEWS FROM THE DRESSING ROOM
Leyton Orient manager Russell Slade told BBC London 94.9:
"They played well in the first half hour but we were very poor.
"We were excellent in the second half but unfortunately we conceded a goal with 15 minutes to go which probably clinched it for them, even though we kept trying to rally.
"We were unfortunate not to get back in the game at 2-1 as it was one-way traffic.
"The goals we conceded were not characteristic of us. They were poor goals and not goals you want to be conceding if you want to be in the shout for a spot in the Championship."
Bristol City manager Steve Cotterill told BBC Radio Bristol:
"We came out the traps tonight and did really well.
"I'm so pleased. This has been a long, hard slog, these six games in 17 or 18 days.
"We've been on the road, the bus, staying in hotels and it's been a tough few weeks.
"Thankfully tonight we've got our rewards. Now we have to look forward to what will be our biggest game of the season [against Tranmere]."
Leyton Orient 24 Jalal 05 Cuthbert Booked 03 Sawyer Booked 04 Vincelot 06 Baudry 15 Clarke 11 Odubajo 21 Bartley (Ness - 78' ) 23 Dagnall (Mooney - 64' ) 09 Lisbie (Lasimant - 83' ) 07 Cox Booked Substitutes 08 James 10 Mooney 12 Larkins 19 Lasimant 22 Loza 25 Simpson 29 Ness Bristol City 30 Moore Booked 35 Osborne Booked 17 Cunningham 03 Williams Booked 05 Flint 18 El-Abd 21 Pack 08 Elliott 10 Emmanuel-Thomas 09 Baldock (Gillett - 90' ) 23 Barnett Substitutes 01 Fielding 02 Moloney 14 Reid 15 Bryan 19 Pearson 27 Burns 34 Gillett
Ref: Carl Berry