McInerney's near-miss, off a pass from from Union teammate Justin Mapp, came just 3 minutes after the Timbers' Kenny Cooper failed to bury the ball in the Union goal at the end of Portland counterattack.
For Philadelphia it was another missed chance for a home win in its push for the playoffs. The tie ran Philadelphia's winless streak to eight straight games.
Rookie Philadelphia goalkeeper Zac MacMath made several key stops before halftime to keep Portland off the board.
Portland is unbeaten in its last three matches.