Last year's beaten finalists Wellington remain on track for another crack at the Air New Zealand title after subduing a gallant Tasman side 22-14 in Blenheim on Friday.
The Lions secured second spot on the standings behind Canterbury and will host Southland in one semi-final next weekend while Tasman face a battle off the field to survive another season.
The Lions will play in their fourth consecutive Air New Zealand Cup semi-final and their second in succession at home, after qualifying top last year and then earning a home final.
But they were made to work hard for their win against a Tasman team that played with passion contributed to a determined struggle throughout the contest.
Tasman outscored the Lions two tries to one, but Wellington's goal kickers Fa'atonu Fili and Piri Weepu, made the most of their kicking opportunities to stay ahead of the home side on the scoreboard.
The match remained close right up to the final few minutes, but Wellington's greater balance of territory and superior discipline eventually paid off and Weepu, playing in his 50th game for Wellington, landed two late penalties to make sure of the winning result for his side.
Tasman had kept themselves in reach of the Lions when reserve hooker Daniel Perrin came up with their second try from a line-out drive in the 69th minute. Tasman captain Andrew Goodman added the conversion to close the gap within two points of the Lions (14-16).
But Weepu's second penalty of the night pushed Wellington out to a five-point advantage and they held on for their fifth victory in a row and their ninth from thirteen games of the regular season.
Previously, both sides had scored one converted try apiece with Fili slotting two extra penalties as the Lions led 13-7 at half-time.
After a lively start, Lions lock Daniel Ramsay was on hand at the end of a fast chain of hands to score the game's first try after 16 minutes, running in support of centre Alapati Leuia and wing David Smith who combined near the touchline.
Fa'atonu slotted the conversion from the sideline to put Wellington ahead 7-0.
Tasman drew level two minutes later with a converted try to centre James Marshall, who ran on to a clever grubber kick by Goodman behind Wellington's defensive line.
Fili replied to Tasman's opening try with a penalty on 22 minutes, and another on the stroke of half-time to take the Lions to their six-point lead at the break.
Despite the absence of any further first-half scoring, the remaining passages of the opening 40 minutes were fast paced as both sides showed a willingness to play in space and keep the ball in play.
Tries: Marshall, Perrin
Pens: Fili 2, Weepu 3
Tasman: 15 Robbie Malneek, 14 Blair Cook, 13 Kade Poki, 12 Andrew Goodman, 11 Afeleki Pelenise, 10 James Marshall, 9 Shaun Begg, 8 Mark Bright, 7 Zane Winslade, 6 Daniel Crichton, 5 Alex Ainley, 4 Glen Gregory, 3 Tristan Moran, 2 Quentin MacDonald, 1 Sakaria Taulafo.
Replacements: 16 Daniel Perrin, 17 Hamish Cochrane, 18 Daniel Hyatt, 19 Jonathan Poff, 20 Ammon Matuauto, 21 James Kamana, 22 Lucky Mulipola.
Wellington: 15 Apoua Stewart, 14 David Smith, 13 Robert Fruean, 12 Shaun Treeby, 11 Hosea Gear, 10 Fa'atonu Fili, 9 Piri Weepu, 8 Mathew Luamanu, 7 Serge Lilo, 6 Victor Vito, 5 Daniel Ramsay, 4 Jacob Ellison (c), 3 Anthony Perenise, 2 Ged Robinson, 1 Arden David-Perrot.
Replacements: 16 Dane Coles, 17 Mark Reddish, 18 Polonga Pedro, 19 Scott Fuglistaller, 20 Alby Mathewson, 21 Conrad Smith, 22 Buxton Popoalii.
Referee: Matthew Stanish