Muscat: Seeb stunned defending champions Al Nasr 2-1 with a last-minute goal from Souri Ibrahima (120th minute) in the His Majesty's Cup last 32 round on Wednesday.
Big guns Al Suwaiq also crashed out against Al Bashayer 5-4 on penalties.
In other matches, Harib al Saadi's third-minute goal had no reply from Muscat as Dhofar advanced to the last 16 stage and Majees accounted for Al Nahda 1-0 in another upset.
Chris netted for Majees in the 86th minute.
Oman club thrashed Nizwa 5-0 to advance, while Yankul blanked Al Wusta 2-0. Elsewhere, Al Arouba beat Ahli Sidab 2-0 to move into last 16.
Oman Observer is now on the WhatsApp channel. Click here