Eddie Jones has conceded that his alterations failed to have the desired effect as England were left to hold on against Wales.
The Red Rose were well in control of what had been dubbed the Six Nations decider at Twickenham, before a late onslaught from the visitors set up a tense finale.
England held on to pick up their fourth win on the bounce in the competition, meaning that only a heavy defeat against France next weekend will deny them a first title since 2011.
"We made a number of changes on purpose to test players and to test the strength of the team [later in the game] and maybe those changes didn't work," Jones is quoted as saying by BBC Sport.
"If you look at our first 60 minutes there was some fantastic rugby. The Grand Slam is a reality and we can't wait to get to Paris and to do the business."
England last tasted Grand Slam success 13 years ago in 2003.
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