Lancashire's hopes of a third successive victory were denied by a defiant Sussex rearguard action at Hove.
Ed Joyce and Naved Arif both scored centuries as Sussex batted through the final day. Opener Joyce occupied the crease for 98 overs for his 140 runs, but when he was eighth out on the stroke of tea Sussex only led by 66.
Amjad Khan fell for the addition of just three more runs but Pakistan-born Arif made a maiden century in only his second Championship game, adding an unbeaten 90 for the last wicket with Monty Panesar.
There were 10 overs left when the players shook hands after Arif, 29, had gone to his hundred by sweeping Steven Croft for four. Sussex closed on 455-9, a lead of 155.
Lancashire's hopes were not helped when former England seamer Sajid Mahmood had to be taken out of the attack for bowling his second beamer of the innings at Joyce, just after Lancashire had taken the second new ball.
With skipper Glen Chapple struggling because of a sore ankle and forced to cut his run-up, Lancashire lacked penetration on a flat pitch which offered very little for the bowlers, apart from some slow turn for left-arm spinner Gary Keedy, who tolied through 55 overs for a return of 4-200.
Sussex captain Murray Goodwin struck the 64th hundred of his first-class career on Thursday as his side fought to save their County Championship match against Lancashire at Hove.
Goodwin's innings of 113 was not enough to prevent his side from conceding a first-innings deficit of 300 after they were bowled out for 290. But Ed Joyce and Chris Nash took the follow on to 147-0 at stumps, leaving them with every chance of taking a draw.
Resuming on 97-4, the home side soon lost nightwatchman Amjad Khan. However, Luke Wright (33) and Andrew Hodd (28) respectively added 81 and 90 with Goodwin before Hodd's departure prompted a collapse.
Sussex lost their last four wickets in 6.4 overs for just 19 runs, with Goodwin mis-timing a back-foot drive to the covers to become one of Glen Chapple's four victims.
Nash and Joyce dug in after tea, however, helped in no small part by Lancashire's seamers conceding 20 runs by regularly over-stepping.
Lancashire continued their excellent early season form to leave Sussex in a big hole by stumps on day two at Hove.
The home side slumped to 97-4 in response to Lancashire's first-innings effort of 590, spinner Gary Keedy (2-30) taking two of the wickets to fall.
The Red Rose county resumed at 322-6 in the morning and, thanks mainly to a second first-class century from Gareth Cross, were able to power on well beyond maximum batting points.
Cross, who became the county's first-choice wicketkeeper after Luke Sutton's winter departure for Derbyshire, struck 125 from 190 balls, including 13 fours and five sixes.
He received solid support from Luke Procter (89), Farveez Maharoof (29) and skipper Glen Chapple (35no), while Sussex seamers Rana Naved-ul-Hasan (3-95) and Naved Arif (3-123) each persevered to take three wickets.
Sussex stumbled badly in the final 33 overs of the day, losing Ed Joyce (21), Chris Nash (12), Luke Wells (19) and Ben Brown (7) during a collapse from 46-0 to a closing position still 293 behind with only six first-innings wickets remaining.
First Division leaders Lancashire made a strong start against Sussex, reaching 322-6 at stumps on day one at Hove.
Karl Brown - who made his maiden first class century against Sussex at Liverpool earlier this month - took up where he left off then by top-scoring with 88 .
It was a tough day for the Sussex bowlers on a sluggish pitch until Rana Naved-ul-Hasan took two wickets in four balls in the penultimate over.
Openers Paul Horton and Stephen Moore justified skipper Glen Chapple's decision to bat first by posting a stand of 129 in 36.1 overs - Lancashire's best opening partnership since September 2008.
That was finally broken 20 minutes after lunch when Luke Wright nipped one back off the seam to trap Moore for 49.
Horton followed in the 45th over for 78 when he mis-timed a pull at Naved and the ball looped off the top edge to Ed Joyce at slip.
Lancashire continued to progress smoothly, before Brown was well caught low down at slip by Joyce for 88 off 161 balls, including 11 fours.
Nightwatchman Gary Keedy was caught behind three balls later without scoring to give Naved his third wicket.