Defoe shone after coming on in Saturday's 1-0 win at Wembley in England's final warm-up match before the European Championships and was unlucky not to score when he hit the post.
The Tottenham man is likely to be Roy Hodgson's fourth-choice striker to start matches at Euro 2012 but he proved on Saturday he may just be the new manager's best option to change a game from the bench.
Defoe has pedigree at coming to his country's rescue, having done so during their doomed 2010 World Cup campaign by scoring the goal against Slovenia that saw them avoid an even more humiliating exit than they ultimately suffered.
The 29-year-old could yet do the same again in Poland and Ukraine and he said: "I'll try my best.
"It's important to have that at a tournament - not only players that actually start the game, players that can come on and make an impact - especially in tournaments when some games go down to extra time.
"You get to semi-finals and, hopefully, finals and then fatigue kicks in."
He added: "You've got to just stay focused on the bench. You might get a chance to win the game - you never know.
"So, it's important just to keep sharp, watch the game as you're not playing and get on and try to make an impact. I believe I can do that."
Defoe has struggled to hold down a starting place at Spurs and may not even have been in the England squad had Fabio Capello still been manager.
The Belgium game was the frontman's first for his country for more than a year.
"It has been a while," said Defoe after his 47th cap - a record 30 of which have been earned as a substitute.
"It's always nice to play for your country. I was delighted to get on."
He added of his close shave: "When I got the shot off, I thought it was in. But, I suppose I'll take that. Hopefully, when I get over there, that one will go in."
Defoe's last trip to a major championships two years ago saw England feted as one of the favourites.
Not so this time around, but he said of the current squad: "It's probably a better mix.
"A lot of the younger lads have come through, which is really good to be honest - a lot of energy.
"After the season, we had a little rest - 10 days off - so I think that helps as well.
"There's always going to be pressure, not only in championships - the games in general. We're a great footballing nation. We've got great players.
"It's important for the players to just enjoy it. This is why you play football - to play for your country and to play in major tournaments.
"The manager said to us, 'Go there and just enjoy it and do the country proud'.
"There's a really good feeling representing your country at a major tournament. Having played the one before, having experienced it, you just want it again.
"Hopefully, this time around, we get off to a good start and we do well because I think everyone deserves it."