The Crusaders survived a rally by 14-man Lions to triumph 25-17 in Johannesburg on Saturday and win a record-extending eighth Super Rugby title.
The match took a decisive turn just before half-time when Lions flanker Kwagga Smith was red-carded for tackling airborne Crusaders fullback David Havili.
An already dominant visiting team stretched a 12-point half-time lead to 25-3 before the home side rallied with two late converted tries.
"You were not in a realistic position to contest for the ball," South African referee Jaco Peyper told Smith before sending him off.
A debatable yellow card by Peyper against 2016 Player of the Year Beauden Barrett had helped the Lions defeat another Kiwi side, the Hurricanes, in the semi-finals.
Victory for a clinical, disciplined and defensively brilliant Crusaders outfit brought a first Super Rugby title since 2008.
It was a second successive final loss for the Lions, who fell by 17 points to the Hurricanes in New Zealand last year.
Defeat robbed Lions coach Johan Ackermann of a fairytale farewell as it was his last match in charge before taking over English Premiership club Gloucester.
"It is amazing," said Crusaders skipper and lock Sam Whitelock. "I am just so proud of the boys.
"The whole group has been working hard this year and it is not just the boys here - it is the guys at home, the supporters, our families.
"We just believed in ourselves, started the season really well and the energy the whole team brought was amazing.
"I would hate to know how many tackles we made this evening, but the boys showed the true grit that I knew they had."
Lions skipper and flanker Jaco Kriel said: "We desperately wanted to give our coach a winning farewell, but it was not to be.
"We respect Johan so much and wish him all the best in England.
"Well done to the Crusaders - we knew it was not going to be easy against them."
Crusaders broke the early deadlock after eight minutes with a turnover offering winger Seta Tamanivalu a chance to dart unopposed from his half and score.
Flyhalf Richie Mo'unga converted and the Christchurch outfit were seven points ahead as they sought to avoid losing a third final since their 2008 triumph.
Lions seemed rattled by the setback and fell further behind on 12 minutes when good work by centre Ryan Crotty and hooker Codie Taylor set up centre Jack Goodhue to score.
Mo'unga saw his second conversion drift across the posts and wide and Havili was also off target with a long-range penalty attempt.
Lions finally got points on the scoreboard after 27 minutes as leading 2017 Super Rugby scorer and fly-half Elton Jantjies slotted a penalty.
The South Africans had another, easier penalty opportunity soon after, but opted to kick for touch in the hope of scoring a pushover try.
But the gamble backfired thanks to a Crusaders turnover and then the match took a decisive turn in favour of the New Zealanders when Smith was red-carded.
Almost immediately a seven-man Lions scrum was pushed back, penalised, and Mo'unga kicked a penalty for a 12-point half-time advantage.
The last thing the depleted South Africans needed early in the second half was to concede another try, but that is what happened.
Crusaders took the ball within a few metres of the tryline, then spun it along the line and No. 8 Kieran Read scored with Mo'unga converting.
The flyhalf then stretched the lead to 25-3 with a penalty and a rout seemed in prospect.
But the Lions rallied and hooker Malcolm Marx and replacement prop Corne Fourie barged over for tries and Jantjies converted both to give the scoreline a respectable look.
Tries: Marx, Fourie
Cons: Jantjies 2
Tries: Tamanivalu, Goodhue, Read
Cons: Mo'unga 2
Pens: Mo'unga 2
Red card: Lions: Kwagga Smith (39 minutes)