Toby Bedford's hard tag on dual Brownlow Medallist Lachie Neale wasn't enough to stop a come from behind Brisbane Lions victory, after Greater Western Sydney crumbled under pressure to let significant time in front slip away amid a heartbreaking second consecutive finals defeat for the Giants in Sydney.

The Lions trailed by 44 points midway through the third term and up to 31 points early in the fourth to grab a dramatic 15.15 (105) to 15.10 (100) semi-final triumph for an elated berth in next Saturday's preliminary final against Geelong at the MCG.

In an unfathomable tale that will grow undoubtedly grow further over the coming offseason, the Giants lead strongly in both finals for all but 19 minutes out of a possible near four and a half hours after succumbing to crosstown rival Sydney by six points at the SCG a week earlier.

GWS also conceded the last nine goals combined from the encounters, including the Lions match-winning final six in a row on the Giants' home turf, to ensure there would be no repeat cameo appearance from Bedford's uninhibited mum, Mel, who celebrated a prized final win on live TV last year in the corresponding match against Port Adelaide.

The pre-match tactical talk was that Bedford's return from a troublesome calf injury that kept the Giants go-to-tagger sidelined for the Sydney Swans' final would be the key match-up in curbing the game-winning influence of Neale, the Lions most damaging midfielder, and getting back on track to challenge for the premiership.

But the five-point loss that was as equally dramatic as the cutthroat final of Port Adelaide's win over Hawthorn the night before proved that not even the Kokatha, Guburn and Wirangu man's powers could provide a panacea from losing the finals' double chance.

Bedford would keep Neale to just the 19 disposals, but that shutdown job did not stop Brisbane from winning after Joe Daniher's boot sunk Adam Kingsley's side.

Bedford made his presence known the other way from the start to give Neale plenty to think about after burning the ball through the corridor with Giants veteran Josh Kelly to set up young forward Aaron Cadman with the first goal on the night.

Bedford held the one-time Fremantle gun to four touches but also permitted him three valuable clearances in that first quarter.

Neale normalised his possession rate in the next two terms with 14 more disposals, including the most effective third, but Bedford clamped down in the last to surrender just one more touch.

Bedford generally proved to have too much speed in the battle against the polished Brisbane ball-winner.

Neale attempted to go to other Giants players at times to throw off the Bedford tag to free up his fellow Lions onballers.

As the visitors mounted a 11-goal-to-seven second-half comeback, the close attention turned the other way.

Lions teammates finally began to create blocks for Neale before Bedford copped a lot more physical attention, including some roughing up from the 202cm Daniher, somewhat of a giant compared to the 178cm Indigenous runner via Halls Creek in the Kimberley.

Neale later accepted to lowering his colours, acknowledging Bedford curbed his impact during the uncompromising contest.

"Toby's had a great year doing these roles so I knew it was going to be a tough night," Neale said of the job of Bedford during the TV coverage back in the Lions' changerooms.

Brisbane coach Chris Fagan was relatively unperturbed with Bedford's close-knit marking.

Bedford himself finished the night with six kicks, seven handballs, in addition to three clearances and two goal assists, but most importantly 10 tackles in a sign of the grind it took to shadowing Neale.

"(Neale) lives with that just about every week now," Fagan said.

"I thought he still made a good contribution, even though it wasn't a high-possession game."

On the Lions' side of play, midfielder Callum Ah Chee pulled out an 11 game-high score involvement performance that Fagan was quick to recognise without turning to the stats sheet.

That came from just the 17 effective possessions, including 12 kicks, three marks, three tackles and three clearances.

"I though Cal Ah Chee stood up tonight," Fagan said.

"I just thought he played a great game on (Lachie) Whitfield.

"Cal just contributed a lot to our scoring."

Whitfield was confined to just 12 possessions by Ah Chee.

But the Nyikina and Yawuru man was a little askew in front of goals, contributing 1.3 to the team's 50 per cent accuracy from their 30 shots.

Charlie Cameron did not have his strongest display, however the Lardil and Waanyi man did go on to boot his 400th career goal in the final.

Cameron added 2.1 from limited opportunities, including a slick goal off the ground in the third quarter, amid an overall nine kicks and two handballs that has guided the small forward into his fifth preliminary final in his career with the Crows and Lions.