BACKGROUND: Open-water swimming (OWS) performance relies on reshaping stroke mechanics as race demands escalate toward a decisive end-spurt. How world-class swimmers implement this high-grading strategy in competition remains unknown, whereas establishing such benchmarks is essential to explain the `road to gold` in OWS. This study provides the first normative biomechanical framework for world-class OWS by integrating inter-swimmer benchmarking with longitudinal intra-swimmer profiling of the 2024 5km World Championship (WCH) winner (FONLO); METHODS: Between May 2022 and May 2024, FONLO and 7 other elite swimmers were monitored during 6 and 9 international races, respectively, using an inertial sensor. Cycle-to-cycle stroke rate (SR) and jerk cost (JC) were computed throughout each race and fitted using locally estimated scatterplot smoothing for both top-4 races (n=13), to derive a performance model, and FONLO`s races, with a focus on the final 10-1minutes; RESULTS: During his WCH victory, FONLO accentuated the modelled top-4 J-shaped dynamics by delaying and reducing time spent above mean SR and JC, while displaying larger modulation ranges across all race phases. His poorer performances showed constrained JC variability, whereas his WCH win exhibited maximized stroke mechanics variability, particularly during the end-spurt, with a sharp break in stroke smoothness between the 17th and 16th final cycles (+340%JC) triggering a 27s sprint; CONCLUSIONS: World-class OWS performance requires high technical flexibility as race success is driven by precise phase-specific regulations of stroke mechanics, preserving stroke smoothness until an explosive final sprint. These findings provide actionable insights to inform performance analysis, race strategy and training design
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