By lunch, the visitors were 117 for 1, needing a further 207 runs to win with Fell unbeaten 51 on and Mitchell 53 not out.
The only wicket to fall came in the second over of the day when Ben Hilfenhaus, who took 4 for 67 in the first innings, trapped Richard Oliver lbw for 11 at 17 for 1.
It was an early blow for Worcestershire for whom Alex Gidman will not bat after being struck on the head by Hilfenhaus in the first innings.
However, captain Mitchell and Fell, in particular, made light work of the Notts attack. Fell, who scored 72 in the first innings, reached his 50 off 76 balls, with eight fours, while Mitchell followed suit, shortly after. The skipper struck nine fours and faced 105 deliveries.