Without Trescothick's defiant century, the Ashes heroes - who lurched to 60 for 6 at one stage against the Patron's XI - would have been shot out for an embarrassingly low total.
In their first innings since the 2-1 series victory over Australia - and exactly seven weeks after their Oval lap of honour - Michael Vaughan's team were indebted to the Somerset left-hander's 186-ball hundred as they mustered an unconvincing 256 for 9, having chosen to bat first.
Trescothick's unbeaten 124 was the only score above 9 from any of the top seven as the Patron's team used the new ball well and then began to find movement off the pitch in the middle overs, former Scottish Saltires seamer Yasir Arafat finishing with 4 for 45.
Trescothick was in modest mood with a few observations at his own expense as he reflected on his innings. There was no doubt, though, that he could be happy with his contribution.
"At one stage I had faced well over 100 balls for 40 - so it was like pulling teeth for a while," he said.
Trescothick is well aware there will have to be more of the same over the next seven weeks if England are to have a successful tour.
"I got a bit lucky and had a few close lbws early on. But you can't always come out and blaze it - and it's not going to be like that over here, because the wickets are generally slow," he said.
"That is what we are going to have to adapt to. In England it flies across the square and the outfields are so quick that dead-bat shots go for four sometimes. Here, they don't even make the outfield."
Trescothick was disappointed to see the rest of the top order miss out, although reserve wicketkeeper-batsman Matt Prior (50) helped post a five-an-over ninth-wicket stand of 117.
"It would have been nice if the top order had got a few more runs. Being 60 for 6 is not ideal preparation, but it is still very early into the tour," said Trescothick.
As conditions eased, he began to get the measure of a tiring attack with a series of sweetly-timed off-side shots and pulls off the pace bowlers, and variations of the sweep against the spinners as he hit 16 fours and two sixes .
Even Trescothick needed some early good fortune as Rawalpindi-born 20-year-old left-arm seamer Najaf Shah removed Andrew Strauss and the captain, Michael Vaughan, in a spell of 2 for 16 in nine overs, before Arafat took three wickets in 12 deliveries.
Strauss and Vaughan were both beaten by good pieces of bowling as well as their own misjudgments - but after Kevin Pietersen and Paul Collingwood had gone for the addition of only one run, it seemed that the warning of the coach, Duncan Fletcher, yesterday that batsmen need to learn patience on subcontinental pitches had failed to sink in.
Strauss shouldered arms to a ball from Najaf which held its line to hit off stump from a fuller length than the left-hander had bargained for, and then Vaughan was trapped in front on the crease. Pietersen reacted to the arrival of Yasir Ali at the pavilion end by spearing a drive on the up to be caught at gully off the new bowler's third delivery - and Collingwood went for a duck when he under-edged a pull at Arafat on to his middle-stump, off a ball that might have been better met by a backward-defensive bat.
Ian Bell did not last long before Arafat snaked a full-length ball between bat and pad to beat the defence, and Geraint Jones was soon also bowled by a similar delivery, leaving Trescothick with the tail after barely 25 overs at the crease.
The belated support acts began with Ashley Giles, who dominated a seventh-wicket stand of 38; then Shaun Udal stayed long enough to accompany Trescothick as he passed his half-century. But it was Prior who took his opportunity best, with a 61-ball 50 which contained eight fours as he kept pace with his senior partner without taking undue risks.
Patron's XI v England (Rawalpindi) England won toss (day one of three)
ENGLAND - First Innings
M E Trescothick not out 124
A J Strauss b Najaf Shah 5
M P Vaughan lbw b Najaf Shah 9
K P Pietersen c Asim Kamal b Yasir Ali 2
P D Collingwood b Yasir Arafat 0
I R Bell b Yasir Arafat 2
G O Jones b Yasir Arafat 4
A F Giles lbw b Imran Tahir 30
S D Udal c Ashar Zaidi b Najaf Shah 14
M J Prior b Yasir Arafat 50
A G R Loudon not out 3
Extras (lb4 w3 nb6) 13
Total (for 9, 74 overs) 256
Fall: 1-10 (Strauss) 2-41 (Vaughan) 3-53 (Pietersen) 4-54 (Collingwood) 5-56 (Bell) 6-60 (Jones) 7-98 (Giles) 8-130 (Udal) 9-248 (Prior).
To Bat: L E Plunkett, M J Hoggard, J M Anderson.
Bowling: Najaf Shah 18-6-58-3, Irshad 17-0-64-0, Yasir Arafat 17-6-45-4, Yasir Ali 4-2-2-1, Imran Tahir 12-2-44-1, Bazid Khan 6-0-39-0.