Estonian driver Virves was 7.4sec off the pace of Armstrong at the day's midpoint but pulled a hefty 15.3sec out of his rival at Dafni to move into the lead.
Armstrong responded by whittling that deficit back down to just 3.0sec on the penultimate test before disaster struck on the day's final stage when he was forced to stop and change a wheel.
The swap took less than 1min 30sec but the damage had already been done and, although Armstrong clung onto second, he arrived back to service 1min 21.6sec in arrears with third-placed William Creighton 21.2sec behind.
Greece marks the final round of the 2022 FIA Junior WRC season and double points are on offer. Should the standings remain as they are, Virves is set to become his country’s first-ever champion.