Driving a new-generation Ford R5, the Pole had a trouble-free event and was there or thereabouts throughout the first day of the competition, before picking up the pace during the opening stages of the final leg.
He completed the opening loop of the last day with a 20.6 advantage over Bryan Bouffier, who then tried in vain to reduce the deficit, but only temporarily trimmed the gap before Kajetanowicz posted the quickest time in the second run through Biskupiec.
The Pole, who also claimed his fourth national title in the event, took the rally win by 23.3s.
Bouffier had stormed into the lead having adapted to the tricky conditions best in the opening leg and went on to set the three quickest times through seven of the first day's stages.
The Frenchman had entered the final day with a 16.8s overall lead over Kajetanowicz, but was powerless to stop him from taking control when Bouffier lost time with a broken damper this morning.
Champion-in-waiting Jan Kopecky comfortably claimed the final spot on the podium.
The Skoda driver was left ruing his decision to run first through the first day's stages and went off the road on the second run through Mragowo which promoted Michal Solowow into third overnight.
Despite suffering from a broken propshaft failure on the final morning, Kopecky managed to reclaim his position, which he retained until the finish.
Solowow fell down to sixth at the final hurdle, behind Krzysztof Holowcyzc and Michal Kosciuszko, who fought through the pain barrier as he is still recovering from a fractured vertebra following a heavy landing in Germany last month.
Craig Breen experienced a tough Rally Poland having been blighted by punctures on both days of the event which knocked him firmly out of contention.
The Irishman had dropped down the order to eighth at one point, before clawing his way back up the table and had taken sixth away from Dakar regular Holowcyzc on the penultimate stage before their positions were reversed on the final test as Breen suffered yet another puncture.
Home hero Robert Kubica was forced to retire from the rally with a missing front-right wheel and suspension damage after striking a rock while cutting a corner in first leg's closing Mragowo stage.
Leading positions after SS13: Pos Driver Team/Car Time/Gap 1. Kajetan Kajetanowicz Ford R5 1h58.40.6s 2. Bryan Bouffier Delta Peugeot +23.3s 3. Jan Kopecky Skoda +1m28.4s 4. Michal Kosciuszko Ford R5 +2m14.1s 5. Krzysztof Holowczyc Ford R5 +3m15.5s 6. Michael Solowow Ford RRC +3m17.4s 7. Craig Breen Peugeot 207 +3m33.5s 8. Zbigniew Staniszewski Ford S2000 +3m48.2s 9. Vasily Gryazin Ford S2000 +4m08.0s 10. Maciej Oleksowicz Ford S2000 +4m13.5s
The fifth Intercontinental Rally Challenge was the best yet, and it was Skoda UK driver Andreas Mikkelsen who emerged as champion from a tense five-way shootout at the season finale. Matt Beer reviews the season