On the day Dundee United's chairman attempted to pour oil on troubled waters by explaining at length in a local newspaper interview the rationale behind the decision to sell Stuart Armstrong and Gary Mackay-Steven to Celtic, this performance was the last thing he needed.

The team's first appearance at Tannadice since their departure was not the time to suffer a second successive defeat for the first time this season, only a second home defeat and to fail to score for the first time since that previous home loss to Aberdeen way back on December 13.

In business terms Stephen Thompson's reasoning for selling two such popular players was impeccable to the point of requiring no explanation, but this is football and he felt the need to justify it in terms that empathised with supporters whose disappointment has spilled over into anger.

How he must have hoped, then, that the remaining players would demonstrate their determination to show how much they care too. Instead this was among their most lacklustre displays of the season, inviting the conclusion that this is a critical moment.

Just a fortnight ago, after all, United were cruising into the Scottish Cup quarter-finals having, the previous weekend, earned involvement in a cup final for a second successive season, while Saints, their conquerors in last season's Scottish Cup final, were mourning the end of their defence of that trophy after their loss to Championship side Queen of the South.

How quickly things can change and in many ways, as McNamara, went some way to admitting, these were particularly awkward opponents to have to confront at this point.

"I'm disappointed with the full game to be honest," he said afterwards.

"There was no fluency, it was stop-start, free kick after free kick, but the first goal is always crucial against them, it gives them something to hang onto."

In fairness, at no point could the visitors truly be described as hanging on as Tommy Wright, their manager, rightly noted.

"Overall we dominated large parts of the game and fully deserved to win two nil," he said.

"We probably could have scored more goals. I think we were the team creating the clear-cut opportunities and I'm delighted with the overall performance and getting the three points because probably the teams around us thought this would be a place where we would drop points, but we always feel we have a good opportunity to get points against Dundee United."

They did so against a team that was both radically and Rado-cally different from that which beat Aberdeen in the League Cup semi-final.

Questions having been raised in recent weeks about the form of United's regular goal-keeper Radoslaw Cierzniak his boss may briefly have been congratulating himself for heading from Pole to Pole in his pursuit of improvement when debutant Michal Szromnik pulled off a fine early save, diving right to deny David Wotherspoon.

If so, however, McNamara could have been forgiven for second-guessing himself within a minute when, following the resultant corner, Michael O'Halloran teed up a strike from similar range on the left and struck it powerfully right-footed. While it dipped nastily and swerved late to Szromnik's left, he should have prevented it from going in.

"I wouldn't blame Michal. Rado's been covering a little bit of late with injury. He's played through it and he's taken a bit of criticism, so I thought we'd take him out of the firing line today which with hindsight is probably a good thing," the manager still asserted, however.

If the way they conceded the lead frustrated home supporters so, too, did the guileless directness with which their team responded for the most part, their attacking play lacking the verve that has become their hallmark and the ease with which their intentions were being read meant Alan Mannus did not have a first half save to make.

Losing Armstrong and Mackay-Steven is obviously a factor in that, but so too, they might conclude, was choosing to leave Charlie Telfer and Aidan Connolly, two of the most exciting young talents in the league, on the bench.

The absence through injury of Callum Morris, another hero of the League Cup semi-final win, meanwhile probably played a part in the second goal as United's central defenders reacted much more slowly than O'Halloran to Dave Mackay's well paced and placed early cross from the right which he duly knocked in from point blank range.

That took his tally for the season to double figures, the target set for him by his manager at the campaign's outset, earning him warm praise.

"Michael can be what he wants in terms of where he wants to go in the game and his attitude and application have been superb, but if he plays as he is doing for us he has to work hard as well and I tell him if he does that he'll get rewards," said Wright.

Dundee United (4-3-2-1): Szromnik, McGowan, S Dillon, Fojut, Dixon, Paton, Rankin (Telfer 57), Butcher (B Spittal 57), Ciftci, Dow, Anier (Connolly 69) Subs not used:

St Johnstone (4-4-2): Mannus, Mackay, Lappin (Croft 45), Wright, Anderson, Millar, MacLean, Wotherspoon, Easton, Kane (Miller 72), O'Halloran

Referee: W Collum Att: 7623

Man of the match: O'Halloran