Watkinson, who has only made one first team appearance this season because of a shoulder injury, slammed 87 as an opener in the one-day Aon Risk Trophy match against Notts.
Padiham pro Mark Harvey was also in the runs with an unbeaten 58.
Then he teamed up with Gary Keedy to wreck the Notts batting on another turning Old Trafford pitch.
Watkinson claimed four for 17 from 10 overs with his off spin, while Keedy took 3-13 from 7.1 overs as Lancashire won by 92 runs.
Both have been added to the first team squad which will travel south to Canterbury today for the match against Kent starting tomorrow, with one-day spinner Gary Yates dropping out.
Nathan Wood is also included despite being forced to retire hurt with a bruised foot early in yesterday's match.
Lancashire 253-5 (Watkinson 87, Harvey 58no, Haynes 34no), Notts 161 all out (Welton 63, Keedy 3-13, Watkinson 4-17). Lancs won by 92 runs.
Lancashire (v Kent, Championship) from: Atherton, Wood, Crawley, Fairbrother, Lloyd, Flintoff, Watkinson, Wasim Akram (capt), Hegg, Austin, Chapple, Martin, Keedy.