Smith strolled off the Gabba with 141 after tea on day three, having pushed his team to 328 and a slender lead over England's first innings 302.
England then lost two wickets to be 33 for two and leave an enthralling test match still very much in the balance.
Having had to soak up 326 balls in his slowest ever century, Smith later said he was surprised at how defensive England captain Joe Root had set his fields and that he expected boundaries to be hard to come by further down the track.
All part of the plan, said Broad.
"Perfect. We know the Australians like to score quickly, if we can restrict them from scoring a lot of boundaries then we'll have periods of taking wickets," the wily paceman told reporters.
"The less balls we can bowl at Steve Smith, the more balls we can bowl to batsmen at the other end, and the better for us."
"It must have been one of his slowest hundreds he's scored for Australia.
"We didn't let them get away from us at any stage and we've seen as a batting group, if someone shows a lot of patience and gets stuck in, it can be quite hard to get them out."
Australia's Josh Hazlewood removed Alastair Cook for seven and James Vince for two, but England's rookie opener Mark Stoneman (19 not out) and Root (five not out) survived a nervous period before stumps.
The pair were peppered by short balls from Australia's vaunted pace trio and Root took a sickening blow on the helmet from spearhead Mitchell Starc.
The captain smiled immediately in response, even if dizzy and with ears ringing, and dug in with courage to remain unbeaten at stumps.
"Crucial," said Broad. "You can so easily lose four-five wickets and that’s the test match gone in those sessions.
"Obviously a bit disappointed to lose two wickets but as I said, it could have been a lot worse.
"It was just proper theatre wasn’t it, proper test match cricket.
"Fast bowling, batsmen playing it well, a few blows being taken but tomorrow will be difficult."
(Editing by Amlan Chakraborty)
