WAS it that they showed Arsenal too much respect; was it the disruption caused by the loss of Geremi; or was it that midweek call Steve McClaren received from Sir Alex Ferguson?

Maybe it was down to all three.

Whichever factors came into play, Middlesbrough weren't the side who had beaten Manchester United, Liverpool and Newcastle, and held Chelsea and Everton to draws at the Riverside this season.

With too many men behind the ball, a common trait in their away performances, you could have been forgiven for thinking it was Boro - not championship-chasing Arsenal - who were gripped by a fear of losing.

Having seen his side claim a vital point in their 2-2 title face-off with Arsenal at Highbury last Wednesday, United boss Sir Alex decided to phone a friend in his hour of need, his former No 2 McClaren.

Fergie called in a favour, which went along the lines of: "You owe us one!''

Boro, of course, helped to hand the title initiative to Arsenal late last season when they pulled off a surprise win at Old Trafford. So, it was payback time.

But beating Arsenal, or holding them to a draw, is always a tall order even when Arsene Wenger's double-winners patently aren't at their best.

If McClaren felt under any extra pressure because of his mentor's demand, it showed in his side's display and the formation he adopted, with Malcolm Christie effectively operating as a lone striker in front of Juninho and Szilard Nemeth.

Yes, Boro matched the Gunners in a turgid first half in which chances were at a premium.

But when on-loan Brazilian midfielder Doriva, in only his third Boro game, turned into trouble three minutes into the second half, Thierry Henry pounced to telling effect.

The French strike ace burst clear, cut in from the right and set up compatriot Sylvain Wiltord to sweep home his 12th goal of the season from around 15 yards.

And it was Henry who delivered the coup de grace with a classic 20-yard free-kick eight minutes from time after Ashley Cole had gone down in a crush of red shirts.

McClaren admitted that the absence of Geremi, who lost his ever-present Premiership tag when he was ruled out with damaged ankle ligaments, had forced him to rethink his strategy.

Jonathan Greening was switched to the right of midfield to fill the void, but didn't look comfortable.

"We had to change the system because we were without Geremi,'' said McClaren, who is still trying to secure the on-loan Cameroon star from Real Madrid on a permanent basis.

"We missed him, but there wasn't much to choose between the teams. Both sides defended well. Arsenal usually create chances galore, but we limited them, so it's disappointing to lose.

"That said, the pressure on Arsenal to win was intense, and they handled it well.

"But you can see the progress we've made from last season when we lost 4-0 and didn't really give them a game here. The biggest progress is our quality of football. They are the first top-six side to win here this season.''

The Gunners are also only the second side to win on Teesside this term; Aston Villa claimed a freakish 5-2 victory in January, and Saturday witnessed the end of Boro's eight-match unbeaten run since then.

Ray Parlour, recalled to the Gunners' midfield in the absence of the injured Patrick Vieira, and skipper for the day, enjoyed a hugely influential performance.

Sent off here on the opening day of last season in McClaren's first competitive game as a manager, Parlour admitted his side were wary of their Riverside visit, and relieved to come away with the points.

"A lot of teams have struggled here, and a lot of people might have thought we would slip up,'' said Parlour.

"Middlesbrough are a good side and they have a good home record. We looked at the game as one where we might be in trouble. This was a possible stumbling block, but we got over it.

"I meant a lot to be captain - it was a great honour.''

Henry, whose 30th goal this season was also his 110th in his 200th game for Arsenal, echoed Parlour's sentiments.

"A lot of people expected us to fail here, so it's a very big win,'' he said. "It's nothing to do with the frustration we felt from Wednesday - we just wanted to win.

"If you'd told me after my first match that I would have 110 goals after 200, I would have laughed at you.''

Whether Henry and Arsenal will have the last laugh in the title race remains to be seen.

Man. United are still three points clear at the top, but the Gunners have that game in hand and, as things stand, are one better off on goal difference.

McClaren certainly won't be waiting for a courtesy call from Sir Alex this week.

The Boro manager's message to his old club was clear. "It's up to them now,'' he said.

Read more about the Boro here.