The Baggies were on the losing end of a 3-0 scoreline at Stamford Bridge.
Alan Pardew's side should have been awarded a penalty early in the contest when Jay Rodriguez, who replaced the injured Daniel Sturridge three minutes after kickoff, was brought down in the box by Cesc Fabregas.
After the game, while speaking to BBC Radio 5 live, Foster said: "It was a decent performance, we plugged away and couldn't find the back of the net. It's similar to how the season has gone.
"It's really difficult - you see some of the results go against you and you're cut adrift. We have big games against other teams in the bottom half of the table - they're really big six-pointers."
The Baggies are rooted to the bottom of the Premier League table following just three wins in 27 fixtures.