EARTH CITY, Mo. -- An early morning wake-up call from St. Louis Rams offensive line coach Paul Boudreau early last week left offensive lineman Greg Robinson wondering what, exactly, he had done wrong.

"I thought I was in trouble or there was something wrong," Robinson said, laughing.

In retrospect, Robinson can laugh at his reaction because Boudreau had invited the draft's No. 2 overall pick to his office with nothing but good news to offer. After a five-week wait, Robinson was getting the promotion he'd been waiting for in time for Monday night's game against the San Francisco 49ers.

Boudreau's message to Robinson was simple, instructing the young lineman to keep the pending move to himself and begin preparing for the challenge that Niners defensive lineman Justin Smith represented.

"He said, ‘We’re going to start you,’ so just continue to prepare and keep it to yourself," Robinson said. "I didn’t want to get too high so I was just preparing and working hard throughout the week like I’d been doing."

Robinson took the overwhelming majority of the snaps with the first-team offense throughout the week, a sure indication to those paying attention to practice that he was about to start. Sure enough, Robinson stepped in at left guard against the Niners with Rodger Saffold shifting to right guard and veteran Davin Joseph heading to the bench.

As you'd expect, Robinson had his share of ups and downs in his debut, but considering he was matched up against Smith, his debut effort was mostly impressive. He was particularly solid when on the move pulling in the run game, but also had a few hiccups along the way.

The Niners blitzed a little more than expected and targeted many of those blitzes on the inside. Robinson failed to slide to the right in time to help on an overload blitz early in the game which helped lead to the Niners' fourth sack but it wasn't all that egregious. And Smith shocked him a couple of times with his strength, including on one play that resulted in a gain of just 2 yards (though it went for a first down) by Tavon Austin.

But overall, Robinson played at a level that was about what was expected and certainly didn't make any mistakes that were particularly damaging.

“He was physical and athletic," coach Jeff Fisher said. "He was in the right place more times than we thought. I thought he played pretty well. He matched up. You have to ask Justin what it’s like to play against him, because it was a pretty good matchup there.”

Because we don't have access to Smith, we can go on Smith's comments to Robinson after the game as relayed by Robinson himself. Robinson said Smith told him "good game" and instructed him to keep working hard.

"He caught me off guard a few times," Robinson said. "It’s just something I wasn’t ready for. Early in the game he did hit me a few times and I was like, ‘Whoa, I’ve got to catch up.’ But I adjusted well."

For what it's worth, Pro Football Focus graded Robinson as the Rams' best offensive lineman in the game with a grade of plus-1.5, and a plus-1.3 in the run game. Of course, Robinson's solid first outing was enough to make many wonder why he played just 10 snaps in the first four games.

Now that he's in the lineup, Robinson doesn't look at his first quarter of the season apprenticeship as a frustrating time so much as a valuable learning experience.

"Honestly, Week 1, even though I wanted to play as bad as I wanted to, I really wasn’t ready," Robinson said. "So I think this whole process was set up to be what it is now, and I think it has paid off."

Robinson has plenty of work to do and says he's prepared to play tackle should the need arise. But for now, he's happy to be settled in with a full game's worth of snaps under his belt.

"I think it’s actually helped me with learning the offense, playing the guard position because there’s more you’ve got to know and it’s not just you out there on an island by yourself at tackle," Robinson said. "So I think it helped me a lot with the offense and each day I’m trying to learn and get better."