England manager Roy Hodgson insisted "the job is only half done" after victory over Montenegro left them needing to beat Poland on Tuesday to secure World Cup qualification.
Montenegro were beaten 4-1 at Wembley, but Ukraine's win against Poland means England must win their final qualifier to confirm their place in Brazil next summer.
Hodgson said: "We know what we need to do. If we want to qualify directly we must beat Poland and this will be a very difficult game."
England top the group with 19 points, one ahead of Ukraine going into the final round of matches.
The 66-year-old added: "I watched the first half of their game against Ukraine before we went out to play and they played very well. If they play as well as they did in that half it will not be easy for us."
Hodgson remains confident England will complete that job but knows anything less than victory is unlikely to be enough with Ukraine facing the relative formality of recording a win against San Marino in their final game.
"I always back the players," said the former Fulham, West Brom and Liverpool boss. "I trust them. We are unbeaten in nine games in qualifying and I think we are quite capable of going unbeaten through the 10th game against Poland.
"With all the talented individuals we have I have got to back them - I would be foolish not to."
Tottenham winger Andros Townsend, 22, took the man-of-the-match honours on his full debut, scoring England's third goal in an outstanding display.
Manchester United's Wayne Rooney put England ahead before Branko Boskovic's own goal brought the second. Dejan Damjanovic pulled a goal back for Montenegro before Townsend and an injury-time penalty from Daniel Sturridge wrapped up the win.
"Andros made a big impact," added Hodgson. "He must be delighted with that because it can't be easy for a young player making his debut for England in a game of that nature.
"He deserves the credit. He played with a calmness and composure that I have seen him play with at QPR and more recently at Tottenham and I was fortunate he was able to reproduce it tonight."
Townsend told BBC Radio 5 live that he only found out about his selection at lunchtime on Friday.
"I'm over the moon, on top of the world," he said. "It was a great debut and great goal.
"Every time Roy has spoken to me, he says he has watched me at Spurs and wants me to do the same thing for England.
"He wants me to get on the ball, dribble with it and make things happen. Thankfully I had a hand in the first goal and scored the third."
Townsend's selection, alongside Sturridge, Rooney and Danny Welbeck, was a surprise - but one which England captain Steven Gerrard believes paid off.
"When new lads come into the set-up, it's important they show no fear and that's certainly what Andros did tonight," said the Liverpool midfielder, who won his 106th cap.
"It was a magnificent debut - not just his goal, which was first-class, but his performance was top-drawer too.
"Roy's selection was very bold - he played with three forwards and a winger - and it paid off.
"We're exactly where we want to be and if somebody had told me before the qualifying campaign that we'd need to beat Poland at home to go to the World Cup I would have taken that."