Hibs made the early running and John Rankin's low drive was gathered by Saints goalkeeper Enckelman, who then claimed a dangerous looking cross by de Graaf.
Riordan then spurned a great chance to break the deadlock, taking a superb pass from Edwin De Graaf but his effort lacked conviction and was easily gathered by Pernis.
Goodwillie tapped in his second after 35 minutes, but Sol Bamba struck from close range just before the break and Paul Hanlon turned home an Edwin de Graaf cross.
The rest of the first half only rarely threatened to excite and de Graaf's powerful shot from 25 yards that was held by Enckelman was the only other chance of note before half-time.