Lee is not new to stuffing Pommie ambitions. In July, at Scarborough, his 134 against the then leaders, Yorkshire, so rattled the Tykes that they plunged to three successive defeats. Yesterday's innings was not quite in that class but it might have removed Derbyshire from their place as favourites.
It was a day of surprises,starting with the pitch which, defying all predictions of increasing lift and turn, rolled out flatter than on the two previous days. Hardly a ball did more than the expected all day.
Somerset still needed another 136, with four wickets gone, to avoid a follow-on but true to character treated the occasion not so much as a crisis but a rollicking adventure. Richard Harden and Jeremy Batty added 37 in 17 overs, the nightwatchman contributing 25 while Devon Malcolm was conceding 34 in six overs.
Andrew Harris was again Derbyshire's best; he eventually had Batty caught at third man - and should have had Harden, when 26, also caught there - a departure that brought in Lee who immediately lifted the contest to a higher level. He has a hawk's eye for the slightest error in length and line and among his initial scoring strokes was a disdainful flick off his eyebrows that sent Malcolm over the on-side boundary.
By his 50, off 76 balls, he had also driven or cut six boundaries and it was clear that Derbyshire were a bowler short, Dominic Cork limping with a hamstring that was "not serious" according to the dressing room. He still managed an adroit piece of fielding to run out Harden.
Dean Jones turned to spin at both ends - when did this last happen with Derbyshire ? - with Kim Barnett adding leg-breaks to Glen Roberts' left- arm slow but by then Lee was in full flight. He was ninth out, caught on the third man boundary, his 110 coming off 138 balls, his fourth century of the summer, his aggregate topping 1,700. He gave one chance, off Malcolm, when 77.
When Derbyshire batted again their huge lead had been whittled down to 60. Barnett, now revelling without responsibility, stormed away again and although he lost partners at 17 and 79 he had his captain's support in reaching a 49th century. In contrast with Lee's, it was measured and predictable, consumate work from the old pro.