。
More spectators came than expected.
Literal
Prediction-more-than many-[appositive-の] spectators [subject-が] come-[past-progressive-ていました].
予想以上に ('more than expected') combines 予想 ('prediction') with 以上 ('beyond, above') and the adverbial に — a fixed phrase for 'exceeding expectations.' The ~ていました past progressive frames the arrival as an ongoing state observed at a past moment. 観客 is the standard word for an audience or spectators at a public event.