Shortly after, Youngs went down with what looked like a nasty knee injury after his left leg appeared to get trapped in the ruck.
Youngs equalled Matt Dawson's England record for the most starts at scrum-half on Sunday, but scans on Monday may well confirm he will miss the rest of the championship if England's worst fears are realised.
No 8 Simmonds was highly impressive on his Six Nations debut and ran in a second late on, although the Exeter Chiefs ace may have to share the headlines to Watson after their eye-catching doubles in the 15-46 victory.
The only negative note for England was an injury to Ben Youngs. Eddie Jone's men have been impressive in the run-up to the tournament, thrashing Argentina and Samoa in November previous year, and are sure to be full of confidence at the Stadio Olimpico.
Nevertheless, an Italy side where seven players were making their tournament debuts, while veteran Alessandro Zanni was winning his 100th cap, hit back with a 20th-minute try.
'He's fitted into the team well.
"I was really pleased with the effort today ... we were completely dominant in the scrum, our lineout was good and then at the end we were able to score tries with some lovely ball movement".
Normal service was resumed six minutes later, though, Farrell bursting through a gap to go under the posts and successfully converting for the first time as Italy's fragile defence was breached a little too easily once again, but an Allan penalty reduced the deficit to 17-10 at halt-time.
Italy have finished bottom of the Six Nations for the last two seasons without picking up a single point. I don't think we've scrummed as well as that in the time I've been in charge of England.
"It is good that we built throughout the game, we felt like we were getting better and better", said Farrell.
Italy coach Conor O'Shea will have seen much to convince him his side are improving in his second year. "We'll train tomorrow, have Tuesday as a recovery day and we feel like we'll be ready by Friday to face Wales", he said.
This is no surprise as the pressure on the Italians has eventually told and England have opened them up as they exhausted during the latter stages. "We played against a great side, No 2 in world, and we caused them a lot of problems with the ball".
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