Poulter was just one shot off the lead and facing a birdie putt on the 15th green when play was suspended due to darkness shortly before 8:30pm on Friday evening, a knock-on effect of the four and a quarter hours' play lost to bad weather on Thursday.
He had to settle for a par when play resumed at 7:15am this morning and then bogeyed the 16th after finding a fairway bunker off the tee and failing to get up and down from just short of the green.
A superb long putt on the 17th, where his tee shot to the par three had spun back off the front of the green, helped Poulter save par there, but he bogeyed the 18th to complete a second consecutive 71.
At two over par, the 37-year-old was three shots off the lead held by Phil Mickelson and Billy Horschel - the only two players under par as Merion more than held its own 32 years after last staging the event - with Luke Donald, Justin Rose and Steve Stricker a shot behind.
Poulter, who shares a best US Open finish of joint 12th with Donald at Winged Foot in 2006, said: "Albeit it with two bogeys in the last three holes to finish round two, I'm right there. I'm right in position and let's look forward to what round three and four have.
"I'm three off the lead in the US Open and that's the difference of one hole. You can make birdie and someone can make double. I'm right in position and right there where I want to be. It's going to be a fun weekend."
Seventy three players made the cut, with the third round scheduled to begin in three-balls at 12:15pm local time from the first and 11th tee.
Tiger Woods and Rory McIlroy had been joint 29th when they finished their rounds on Friday but had climbed to 13th without hitting another ball.
At three over par they were only four off the lead and paired together for the third day in succession, with Spain's Gonzalo Fernandez-Castano making up their group.
Open champion Ernie Els was also three over while Florida-based Scott Russell Knox and three-time major winner Padraig Harrington were a shot further back.
Paul Casey, who had to come through qualifying at Walton Heath, was five over after rounds of 73 and 72, while Sergio Garcia was six over after consecutive rounds of 73.
Lee Westwood, John Parry, Paul Lawrie and Martin Laird all finished seven over, while David Howell, Simon Khan and Irish amateur Kevin Phelan all made the cut on the mark.