The Christchurch-based powerhouse handed the Chiefs only a second loss of the season to silence a full house at Hamilton's Waikato Stadium and secure a 14th Super Rugby title of all types.
Hooker Codie Taylor crossed for the second time in the 73rd minute for the winning score and the Crusaders held off the Chiefs, reduced to 14 men for the third time in the match, to snatch the victory.
The Chiefs had tries from fullback Shaun Stevenson and flying winger Emoni Narawa and held a 20-15 lead on the hour mark, but fell short in their bid for a first Super Rugby title since they went back-to-back in 2012-13.
As well as coach Robertson, who will take over at the All Blacks after the World Cup, the Crusaders were bidding farewell to three players who helped build the dynasty in Sam Whitelock, Richie Mo'unga and Leicester Fainga'anuku.
"I'm lost for words, I'm so proud of the effort," said an emotional Taylor.
"I can't get the fact that the boys are leaving out of my head and how much it means to them. It's special. Can't take anything away from the Chiefs. They threw everything at us and we just managed to hang in there."
The Chiefs were the dominant team in the regular season and co-captain Sam Cane, the last of the three home players to be shown yellow cards, was clearly deflated.
"We've had a heck of a season and it certainly hurts to come up short right at the end there," he said.
"A lot of credit must go to a quality Crusaders side. They've been the best for a number of years now and they managed to show that again tonight."
Flyhalf Mo'unga scored a try and kicked 10 points, opening the scoring with his first penalty in the ninth minute, just before Chiefs centre Anton Lienert-Brown went to the sin bin for a dangerous tackle.
Damian McKenzie levelled up the contest with a penalty before Lienert-Brown returned, however, and three minutes later the home side were ahead.
Number eight Luke Jacobson tackled Will Jordan hard in midfield before stripping the ball off the Crusaders fullback and two phases later Shaun Stevenson was cruising across the line for his 12th try of the season.
Jacobson was yellow carded for repeat team offences soon afterwards, however, and Taylor grabbed his first try off the rolling maul against a short-handed pack to cut the deficit to 10-8.
The Crusaders were now in the ascendant again and Mo'unga finished off a raid down the left wing and converted his own try to give them a slender 15-10 lead at halftime.
The Chiefs struck back through Emoni Narawa three minutes after the break when slick hands through the backline sent the winger across in the right corner and McKenzie converted from wideout to nudge the home side back ahead.
The flair that the Crusaders had mostly suffocated in the first half was now unleashed and the noise from the crowd hit new heights as McKenzie kicked a second penalty for a 20-15 lead.
Narawa had a second try called back in the 56th minute and the Crusaders immediately laid siege to the Chiefs line but the home defence held firm.
They were unable to repeat the feat legally eight minutes before full-time and Cane was sent to the sin bin with Taylor mowing over the line from another catch-and-drive a minute later.