Dunlop's latest victory came in Wednesday's Supersport race, which also saw his brother William narrowly miss out on a podium place.
Michael came in 2.3 seconds ahead of runner-up Bruce Anstey, with John McGuinness just one second ahead of William to take third.
The Morecambe Flyer's finish takes his podium tally on the island to 40 - equalling the number achieved by road racing legend Joey Dunlop.
Earlier this week, McGuinness and the Honda team helped mark the 30th anniversary of the first of Joey's record 26 wins at the TT - with McGuinness donning leathers just like Joey's for the occasion.
Poignantly, 30 years on, it is Joey's nephew who has his eye on breaking records.
His four-in-a-row equals the success of another Northern Ireland rider, Phillip McCallen, while further victories in the races still to come this week could see Michael Dunlop match or better the five-wins-in-seven-days streak of Yorkshire racer Ian Hutchinson.
Dunlop's career wins on the Isle of Man now stand at seven - two more than his dad Robert.