Lauren Johnson was second in 2:38.33. Watson ran in third position through 800m, which she passed in 2:08.03, before being passed by Hannah Fields in the final 200m. Fields ran 2:40.18.
Watson's record splits for each 200m were: 30.8, 33.43, 32.19, 31.63 and 32.70.
Before yesterday, Sarah Brown neé Bowman held the record at 2:43.4 since 2005.
The 1K record is Watson's third national high school record of the year. She also broke the records for 600m (1:27.13) and 800m (2:01.78) this season.