(Note: election law forbids publication of polls in Peru a week prior to April 10 voting)
LIMA, April 7 (Reuters) - Peru's select stock index closed down more than 4 percent on Thursday on news that a Datum poll seen by a source showed leftist Veronika Mendoza could face front-runner Keiko Fujimori in a run-off after Sunday's presidential election.
The poll showed Mendoza with 18.5 percent of valid votes, statistically tied with centrist Pedro Pablo Kuczynski's 18 percent. Long-time leader Fujimori had 43 percent support in a mock vote that excluded likely blank and spoiled ballots. (Reporting by Ursula Scollo; Writing by Caroline Stauffer; Editing by Richard Chang)