Assat looked to have put their poor form behind them with a 4-0 win over Jukurit last time out, while Tappara's surprise loss to HIFK yesterday meant a win tonight would see the Aces return to the top of the table.
But Lukko, chasing a place in the top four, were always going to provide a stern test, and so it proved when Jami Krannila put the visitors in front seven minutes in, before Niclas Almari doubled the lead before the first period was over.
The home side made the perfect start to the second period in response, as Jan-Mikael Jarvinen scored 28 seconds in to halve the deficit, but they failed to build on that, before an Antoine Morand penalty and another from Topias Haapanen made it 4-1 to Lukko after 40 minutes.
Alex Beaucage completed the 5-1 win with a powerplay goal five minutes into the final period, as Assat remain two points off the top after a fifth defeat in seven. For Lukko, it's five Liiga wins in a row, and six in all competitions.
It was a good night for Tappara as they stayed top without playing, and a good night for Lukko as that was enough to take them fourth, as the sides beginning the night in second, third and fourth all fell to defeat.
KooKoo have stayed in third, a point clear of the Rauma side, despite a complete break in their recent form, going down 3-0 at the hands of Ilves. Matias Mantykivi and Matic Torok struck in the second period before Lukas Svejkovsky made sure with an empty-netter late on.
But it was Mantas Armalis in the Lynx's goal who was the hero, with 31 saves to inflict just a second loss in 10 on KooKoo, while Ilves have put three wins in a row together, moving into 10th place.
Dropping out of the top four are JYP, as they could only pick up a point at home to Hameenlinna after a shootout loss sealed a 4-3 defeat.
It looked certain to be JYP's night as they came from 3-0 down to level at 3-3 midway through the third period, courtesy of a Daniel Torgersson strike, but they could not press on and find a winner either late on or in overtime.
That proved fatal for the hosts, as Oliver Kopiloff scored what proved to be the decisive penalty in the shooutout, as Hameenlinna ended their five-match losing run by the barest of all margins, yet they remain one place outside the Playoff picture.
Following a run of four defeats, sixth-placed SaiPa have quietly hit back with a five-match winning run, with the latest victory coming on the road against KalPa, where they won a rematch of last season's Playoff Final 6-3.
The visitors trailed 3-2 in the third period, but four goals in the final 14 minutes saw them romp to victory and condemn the Kuopio side to a third loss in a row, leaving them in eighth.