SOFIA (Reuters) - Bulgaria's Socialist-backed candidate, Rumen Radev, led the first round of Bulgaria's presidential election, partial official results showed early on Monday, leading his main rival from the ruling centre-right GERB party.

Radev, 53-year-old former air force commander, led with 26.45 percent of the vote, compared with 21.38 percent for parliament speaker Tsetska Tsacheva, with 10.48 percent of polling stations counted. The result, which reflected earlier exit polls, meant the two would compete in a run-off on Nov. 13.

(Reporting by Tsvetelia Tsolova; Editing by Peter Cooney)