Sammy, the first St Lucian to play Test cricket, showed the value of accurate, seam bowling at a lively, if not express, pace as West Indies bowled out England for 313 in their second innings.
But at the close West Indies were still in danger of going 2-0 down in the four-match series with one to play, reaching stumps on 22 for one - still needing a further 433 runs to reach their victory target of 455.
Sammy's haul included three wickets for no runs in five balls and six for 12 in 33.
The 23-year-old's were the best Test debut innings figures for West Indies since Alf Valentine's eight for 104 at Old Trafford in 1950.
And they were the best by anyone in a Test match at the Manchester venue since West Indies great Malcolm Marshall's seven for 22 in 1988.
Sammy, who took the only wicket to fall in Saturday's first session, when he reacted to quickly to catch England captain Michael Vaughan off his own bowling, said some advice from team-mate Chris Gayle had been timely.
"I remember when we walked out I told Chris something special will happen today, and he said 'yeah? See boy, you have to make it happen.' And I just went along and put the ball in the right areas, and I came out successful.
"I always dreamed of playing for West Indies. I made my debut, first in the one-dayers and now in the Test, but I never thought it would turn out like that," added Sammy, effectively in for dropped batsman Sylvester Joseph.
Sammy enjoyed a purple patch in the 75th over with three wickets.
He squared up Ian Bell, who edged the over's first ball to wicket-keeper Denesh Ramdin and next ball Matthew Prior was also caught behind.
Liam Plunkett survived the hat-trick, the ball just missing the outside edge. But two balls later Plunkett was also out for nought, brilliantly caught by Dwayne Bravo diving forward from second slip.
"The first ball to Ian Bell came out exactly as I wanted it to, then Prior came and it was exactly the same ball. It was just unbelievable how the ball was landing in the right areas. The hat-trick ball just swung too much."
Sammy is now set to loan the ball with which he did so much damage to the MCC Museum at Lord's, although he will be taking it home with him when he returns to St Lucia.
And he said the people of his native island would be rejoicing at his achievements. "I've just been on the phone with the minister of sports, the St Lucian people will be happy today (Saturday)."
They might not be so happy with the overall match situation but Sammy said the game was not yet beyond the West Indies.
"We have Chris at the wicket, we have Shivnarine Chanderpaul to come, Runako Morton, myself. We'll take it session by session and see how far we get chasing down this total."