Valencia striker Batshuayi ended a barren run of club form with the brace, and gave Martinez's men winning momentum ahead of their final Nations League fixture away to Switzerland, where a point will be enough to book a finals berth.
Starting in place of the injured Romelu Lukaku, Batshuayi eventually made his opportunity count as he benefited from Eden Hazard's defence-splitting pass to break the deadlock just after the hour.
The 25-year-old had squandered two chances in the opening 20 minutes, but finished the match on a high thanks to Hannes Halldorsson's gift of a second goal nine minutes from full-time.
"In the first half [Batshuayi] experienced some setbacks," Martinez told broadcaster VTM.
"He moved well for the opening goal. I'm glad he scored twice, but he also played a good game. I was delighted with his overall performance.
"In this type of match you have to remain constantly focused and be able to score a goal with one action."
Belgium struggled to break down relegated Iceland despite fielding a strong 11 for what was essentially a dead rubber, the result not affecting either side's standing in Group 2 of League A.
A hard-earned 2-1 win over Switzerland in October puts the Red Devils in the box seat to advance, but Martinez anticipates strong resistance on Sunday.
"I expect a very difficult game," he said. "The game we had in Brussels showed that Switzerland are a very strong group that have been together for a very long time.
"They are a very strong tactical team that use the players in their best system.
"They are playing at home, they have really good momentum in the Nations League. It is a game we are really looking forward to.
"We expect the same level of performance as in the Brussels game."