Even then the Essex team deserved to take all three points with striker Chris Moore seeing a shot agonisingly ricochet off the inside of the near post deep in stoppage time and crawl along the goal-line only to go out of play.
Blackman scored with a deflected drive from the edge of the box in the 90th minute to put behind him six months of injury woe.
It had seemed Macclesfield would suffer a hangover from the European qualifiers when their Malta international Luke Dimech, returning from a rout against Norway, blatantly and unnecessarily pushed Paul Benson in the back in the fifth minute.
Even though midfield man Glen Southam had to retake his first successful penalty for encroachment, he kept his cool to slot home the second in the other corner.
Macclesfield tried hard to get a grip in the first half but were reduced to long-range shots from Jamie Tolley and Adam Murray which both flew wide.
Their best chance to equalise came in the 66th minute when sub Simon Wiles delivered a telling cross into the six-yard box only for Francis Green to skew wide on the slide.
Macc keeper Tommy Lee kept his side in the game when he pulled off a fingertip save to deny Shane Huke in the 73rd minute.
Macclesfield thought their luck had run out in the 84th minute when skipper Kevin McIntyre floated a neat cross to the near post where Gareth Evans glanced a header off the outside of the far post.