Will Greenwood described England's win against Fiji as 'nervy and inexperienced', but has backed Lancaster's men to bounce back against Wales.
England were only seven points ahead before a penalty and two late tries gave them the bonus point and a far more attractive scoreline.
Though they finished the game in style, 2003 World Cup winner Greenwood was not quite convinced by the start made by England.
"Nervy, tense, inexperienced," said the Sky Sports expert. "The rain affected them; they wanted to play a certain style.
"Having said all that, they grasped the game with 15 minutes to go and came out of it with a bonus-point win, and they will have learned a huge amount there.
"Their precision wasn't right, their accuracy wasn't right early on.
On the players he thought stamped their mark at Twickenham, Greenwood singled out two of Lancaster's replacements.
"I thought Farrell had a massive impact coming on at 10.
"George Ford was tidy, Brad Barritt was poor, so some huge selection issues coming up for England.
"I think Launchbury should start. I think he has an opportunity to be one of the world's best second row forwards given the opportunity and the stage.
"He's coming back from fitness having missed the Six Nations. He's got more game time under his belt - get him in.
Stuart Lancaster picked a strong England team in the World Cup opener, but Greenwood expects to see some changes to the side to play Wales.
"Billy Vunipola to me [is a] street fighter," said the World Cup winner.
"Saracens have had some tough times in European cup finals and he knows how to scrap it out as a dog fighter on the big stages, so I'd bring him back in at 8.
"I personally would go again with George Ford. I thought his performance against Wales in the Six Nations when they were down in the Millennium Stadium on a Friday night was strong enough.
"But I can absolutely understand why - with the impact Farrell's had, the improvement he's got in his passing game, then he knocks over the conversion from Mike Brown's try - his style of play might be more be suited to a World Cup."
Should they make it out of the pool, England's quarter-final opponent will come from Pool B, which on Saturday provided the biggest shock in World Cup history as Japan tore apart the two-time champion Springboks.
It was a result that went against every prediction, but the way they kept fighting back after going behind proves the result was no fluke according to the former England centre.
"The Japanese went behind four times, and kept coming back, and kept believing," said Greenwood.
"They conceded a couple of really daft seven-pointers; they gave the South Africans 14 points with two simple missed tackles.
"So you then start to explore the score and understand it really wasn't an accident.
"Magnificent defensive press from the outside. Unbelievable work at the breakdown where they took on Bismarck du Plessis and Francois Louw - two of the best at it.
"And then an ability in the cool light of day to call a backs move that saw Kotaro Matsushima just walk through untouched, hand over to the legend now that is Ayumu Goromaru, and before you know it you're going crazy. It was an unbelievable day.
"Everyone has been talking about this World Cup being the most open World Cup there's ever been, and Japan downing South Africa in weekend one tells you exactly that.
"Extraordinary bravery from the guys.
"One of my favourite photos I saw on Twitter was of a South African hugging a crying, aged Japanese gentleman who just couldn't believe his eyes!"