From Oliver Naesen's Strava the last loop (~15km) was done at an average speed of almost 50 km/hr (31.0mph). So he did this final 15km about as fast, and there was obviously a bunch of wind (it's a loop so in theory no net effect but as everyone knows TTing is a lot harder combining sections with head- and tailwind than in no-wind). Naesen's reported power, mostly sheltered in the bunch on that last part, was 318W, so Asgreen (who I guesstimate is of similar size as Naesen) must have been putting out some monstrous numbers, like 420-450W, for 18min. Absolute beast mode for sure!
This actually reminded me of VdB in Scheldeprijs 1996... unlike Jungels last year, where it always looked like he would stick it, here it seemed Asgreen was almost cooked at 3 - 4 km, dangling out in full view of the peloton, but somehow he still hung on. Amazing performance.