Lewis struggled in this game, allowing more interior pressures than Nowak had allowed in the five previous games combined. Nowak also had not allowed any hits or sacks on the QB, while Lewis allowed a couple in this game.
The coaches were desperate to get the running game going, with Marshawn back, and Lewis is considered the better run blocker, although Nowak continues to improve and did some nice work as a run blocker last week. I don't think Lewis paid dividends as a run blocker in this game, so I would expect to see Nowak back at center against the 49ers.