Hearts were stung by a second-minute Johnny Russell strike and never truly recovered as they lost to an energetic Dundee United side at Tannadice.
Michael Ngoo hit the United bar with a shot but Hearts lost their captain Marius Zaliukas to injury and had Ryan Stevenson sent off in 25 minutes.
Jamie MacDonald saved from United's Jon Daly but Willo Flood hit a cool second.
Hearts striker Ngoo hit the bar again before firing home in 76 minutes but Michael Gardyne secured the points.
Russell scored in 13 seconds to begin United's defeat of Rangers in the Scottish Cup last week and he was on the scoresheet within two minutes against Hearts.
He controlled John Rankin's low cross into the box from the left, took the ball away from his markers, spun around 10 yards from goal and hammered a low shot past Jamie MacDonald with three white-shirted Hearts players racing to close him down.
Marius Zaliukas's tame effort from a corner was saved easily by United's Radoslaw Cierzniak and until Michael Ngoo cracked a shot off the crossbar in 19 minutes the intervening period was characterised by United's crisp tackling and appetite for the match.
Clearly, Jackie McNamara has made a positive impression early in his tenure at Tannadice.
If being a goal down was bad news for John McGlynn, there was a further blow for the Hearts boss when Zaliukas, having headed the ball clear, landed on Russell's foot and badly twisted his left ankle.
Darren Barr was his replacement.
A goal down and minus their captain, Hearts were hit by a triple whammy when Stevenson was shown a straight red card by referee Willie Collum for a tackle on Gary Mackay-Steven.
The decision seemed very harsh. Stevenson's studs were showing as he stretched for the ball but his tackle was controlled and did not appear to be dangerous. The Hearts midfielder was seething as he left the pitch.
Gary Mackay-Steven was on the ball often down the left wing in the opening 10 minutes of the second half but it was from a cross from the right that United came close to doubling their lead.
Jon Daly slid in to meet the low cross but was denied a goal by Jamie MacDonald's smart block down to his right.
There was nothing the Hearts keeper could do, though, for United's second in 62 minutes.
Flood collected a throw-in out on the right wing, worked his way towards goal and passed to Mackay-Steven, who slipped a pass through a flat-footed Hearts back line to Flood, who had continued his run, and he rounded off the move with a calm left-footed finish from 10 yards.
The little Irishman stung the palms of MacDonald moments after as United looked to demoralise their 10-man opposition.
Ngoo lifted the spirits of the 1,000 or so travelling fans when he hammered a shot off the crossbar for the second time in the match, cutting past Keith Watson and shooting from 20 yards.
And he had them in raptures when he blasted high past Cierzniak from 10 yards when the ball fell to him kindly at a corner.
That gave Hearts 14 minutes to grab an equaliser but it was United who scored the next goal, Gardyne sliding in to force home Jon Daly's teasing cross, thereby adding to the momentum created by McNamara's arrival.