Richard Montgomerie and Murray Goodwin both made big hundreds as 561 runs were scored on the third day at Swansea.

But it is Jason Lewry who has given Sussex a sniff of victory against Glamorgan.

Lewry took 4-28 in 38 balls in his second spell as Glamorgan slumped to 289-7, still needing another 59 runs to avoid the follow-on which would effectively insure them against a sixth successive Championship defeat.

Much depends on David Hemp, who will begin the final day unbeaten on 125. His was the third century of a thoroughly entertaining third day but Lewry's post-tea burst might yet prove to be the match-winning contribution.

Hemp and Australian left-hander Matthew Elliott had put on 172 in just 31 overs after Glamorgan lost Dan Cherry and Michael Powell in the first seven overs of their reply.

Elliott's first seven scoring shots were all boundaries and Hemp lost little by comparison, hitting 14 fours and smashing two sixes off Robin Martin-Jenkins, including an outrageous upper cut over deep cover's head, as he raced to a 95-ball hundred, only the second by a Glamorgan batsman since their promotion to division one.

Lewry removed Cherry in his first over but his more effective work this season has been when the ball has lost its shine and started to reverse-swing.

Sure enough, in his second over back he trapped Elliott leg-before offering no shot after he had struck 15 boundaries and then produced a peach to remove Sourav Ganguly for a third-ball duck, shaping the ball back to hit middle stump.

Hemp and Mark Wallace steadied things for a while but Lewry's slider trapped Wallace on the back foot and Robert Croft was undone by extra bounce, the Glamorgan captain slashing high to slip.

Mushtaq Ahmed, whose first six overs had gone for 52 runs, returned to pin David Harrison on the back leg four overs before the close and Glamorgan had lost five wickets for 61 in 13 overs.

Earlier, Sussex plundered 272 in 48 overs off an increasingly ragged attack before Chris Adams declared 45 minutes after lunch once his side had compiled comfortably their biggest total of the season.

Goodwin reached his second Championship ton in three weeks two balls before Montgomerie lodged his first for more than two years, even though he had given his partner a 48 over start.

It was all too easy for Sussex's third wicket pair to press the accelerator against an attack which seemed to be going through the motions almost from the start. But that should not detract from their respective performances.

Goodwin has seldom played better in five seasons with Sussex as he is at the moment.

After reaching his 21st hundred for Sussex he scored his next 50 runs off just 29 balls and was aiming another expansive drive through the covers when he was caught behind off Croft, having hit 19 fours and a six from 173 balls faced.

It was much harder work for Montgomerie, who grafted for 5hr 42min over his hundred.

But he too played with increasing freedom after reaching the landmark and Adams delayed the declaration to give him the opportunity to score a maiden double hundred.

He settled instead for an average-enhancing red inker' and the highest score by a Sussex batsman in Wales, beating the 161 John Langridge made at Cardiff Arms Park in 1939.

There were entertaining cameos from Adams and Matt Prior before Glamorgan's suffering ended.