Ifill threatened in the opening minute when Cullip conceded possession to him just outside the Albion area.
His path was blocked as he tried to burst into the box between the Seagulls skipper and Pethick leading to optimistic appeals for a penalty from the fans rather than the Millwall players.
Harris now recovered from testicular cancer, went on a dangerous individual run before carrying the ball too far, which allowed Petterson to collect.
Albion were guilty of giving away possession too easily in the early stages.
Roberts got the better of Watson inside the centre circle to send Ifill through the inside right channel.
His angled shot was blocked by the covering Butters at the expense of a corner.
In the seventh minute a free-kick from Roberts was helped on by Nethercott to Claridge, lurking towards the back of the six yard box.
He tried to flick the ball over Pethick and was convinced the Albion rightback handled, but referee Mathieson was having none of it.
Albion continued to come under the cosh as Harris rounded Watson before laying a pass into the path of Roberts in space 20 yards out.
The ex Crystal Palace and Wimbledon midfielder's crisply struck shot was fisted for a corner by the well positioned Petterson.
Butters defended well when Claridge pursued a hoof down the middle by Lawrence.
Albion's recent signing was back pedalling towards the edge of his own area but still managed to cushion a header to a colleague.
Albion, having survived the initial burst from the Lions, began to settle down and press forward themselves.
Pethick, given room to progress from Carpenter's square pass, crossed for Kitson to strike a swivelling right foot volley narrowly wide from 20 yards.
A minute later Brooker took on Ryan and exchanged passes with Kitson before firing well over from just outside the area.
Brooker went into the match as topscorer with his goals at Portsmouth and in the opening day victory at Burnley and it was encouraging to see him in positive mood.
The Seagulls were enjoying much more possession by the midway stage of the half and Melton was getting through some good work on the left hand side of the midfield trio.
The Seagulls broke smartly from Millwall's third corner of the contest. Marney won a tussle with Ifill and fed Brooker down the left flank.
His cross was slightly over hit and the stretching Kitson could not keep his right foot volley on target from beyond the far post, but it was nevertheless a promising counter-attack by Martin Hinshelwood's men.
When Claridge was caught offside from a cross the Albion fans responded with cries of 'Pompey reject'. It was ironic really considering Albion have three ex Portsmouth players in Petterson, Pethick and Butters.
Pethick and Cullip vented their anger at one of the referee's assistants on more than one occasion when they felt he had missed offside decisions.
Ifill was lectured for protesting too much moments later as the exchanges became rather scrappy.
Ifill capitalised on a lot of space in the 35th minute. He cut inside his close friend Watson to hit a low left footer from 25 yards which Petterson was unable to hold.
Fortunately for the keeper Cullip was on hand to clear from Claridge.
Roberts drilled over from Cullip's clearing header shortly after as Millwall re-asserted.
The ever involved Ifill then delivered a vicious right wing cross which caused a collision between Cullip and Pethick. The latter was caught on the right shoulder by his team mate's boot and ended up in the back of the net before swiftly returning to the fray.
Claridge made a mess of the clearest opening so far as the interval approached.
Harris cut a cross back into his path, but he mis-kicked twice with Pethick and Butters close at hand.
Harris and Cullip were involved in a tugging match as Claridge put through his strike partner.
Harris went on to cut inside Cullip in the area before planting a right foot effort the wrong side of the far post.
Albion had another escape a minute from half time. Nethercott and Cullip went up together from Cahill's free-kick and the ball appeared to loop off the head of the Albion captain and against the bar.
The Seagulls were satisfied to go in on level terms. They had a good spell midway through the half, but Millwall started and finished the opening 45 minutes much stronger.
Half-Time: Millwall 0 Albion 0
Albion were controlled in possession at the start of the second half without looking especially threatening.
A deep cross from Pethick was palmed behind by Warner for Albion's first corner of the contest.
It was taken by Watson and cleared at the near post by Ifill.
The Seagulls almost fell behind in the 52nd minute. They looked for an offside flag which did not materialise when Ifill's cross found Claridge unmarked in the centre of the area.
His looping header eight yards out was pushed over by Petterson and from the resulting corner Roberts blazed over from long range.
Millwall captain Nethercott collected the first caution of the match on 55 minutes for a foul from behind on Kitson five yards inside the Albion half.
There was uproar a minute later as Kitson caught Lawrence on the touchline in front of the main stand as the Millwall fullback cleared.
The Millwall players reacted angrily to Kitson's challenge and the home fans were baying for a red card.
Referee Mathieson consulted his assistant before booking the Seagulls' striker.
Kitson was predictably booed the next time he touched the ball.
The next time Ifill touched the ball it almost produced a goal. He ploughed through a challenge from Watson before driving narrowly wide of the far post from 20 yards.
The temperature had risen appreciably on and off the pitch following the incidents involving Kitson.
Millwall made a double substitution on 62 minutes, introducing May for Harris upfront and Kinet for Livermore in midfield.
Youngster May scored in the 1-1 home draw against Ipswich last month, while Belgian Kinet was on target against the Seagulls in that Worthing Cup tie on their last visit.
Millwall were forced into a third and final change with 19 minutes remaining, Bull replacing the injured Cahill.
Bull almost made an instant impact, heading over at the near post from Claridges cross.
Ward made Millwall's supremacy count on 73 minutes with a back header into the net at the near post from substitute Kinet's corner.
Albion were reduced to ten men for the second match in succession on 76 minutes when Pethick was sent off for an incident off the ball involving Kinet which left the Millwall substitute on the ground requiring treatment.
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