His side had gone 27 league games unbeaten before Sunday's defeat.
Clark was a Mackem player in 1998 when Sunderland lost to Charlton on penalties in a 4-4 draw at Wembley.
Lee Clark: "This hurts just as much and that was horrendous.
"I think they didn't deserve 3-0. When people look at that, they'll think it was a one-sided game but it just wasn't.
"I was expecting us to get a goal but they withstood what we threw at them and then hit us with a treble.
"I feel for the players. We knew it was a one-off game and some team had to win it.
"But the players don't have to feel ashamed for anything that's happened this season. They broke numerous records and ran through proverbial brick walls for me this season.
"I'm physically and mentally drained at the moment and I need to recharge my batteries. But I know what it takes to bounce back, I've done it before.
"We've had an unbelievable season but we haven't achieved our goal.
"The biggest thing that's eating away is, not taking anything away from Peterborough and their result, that it's gone 3-0 and it looks so against my team and it wasn't.
"We were in the ascendancy, we had the momentum and we were flying at that time. But this game was about winning, not about how we played.
"It was just a crazy seven minutes. In the second half for half an hour, I thought we were the dominant team. But we knew they had a set-piece expert who has fantastic delivery. And on two of the goals, it was proved right."
A 'THANK YOU' TO FOOTYMAD READERS ...
'MAGPIES IN EUROPE'
FOR £5.99 (inc post)
2010/11 has been NewcastleUtd-Mad's greatest season for page 'hits', and as a thank you to all readers we are giving you the chance (FOR TWO WEEKS ONLY) to purchase "MAGPIES IN EUROPE" for £5.99 (and that includes the postage).
*Normal price is £9.99
OFFER ENDS JUNE 10th 2011
Although "Magpies In Europe" will not be launched OFFICIALLY until next season ... if you want a copy it is available NOW from this website ... and ONLY from this website!
FOREWORD BY FAIRS CUP HERO JOHN McNAMEE
Sports Journalist Richie Everson: "At last a book that the fabulous Newcastle United fans can relate to. It's informative, all the facts and figures are there, plus the 120 match reports from all the fixtures ... but it is the articles by the supporters that amazed me.
"I went to many of those games, and this is the only book I can honestly say 'hits the nail on the head'!
"Yes we know the results and the scorers, but some of the facts in this book had me so wrapped up in it I couldn't put it down.
"Was Benny Arentoft cup-tied when he played in the final? Big Wyn and his battle with John McGrath; McFaul scoring a penalty when the crowd had gone home; the trouble in Palermo; it is all amazing stuff.
"I would honestly give this book 10 out of 10."
MAGPIES IN EUROPE
From Antwerp to Zurich
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