The Magpies fell behind in the 33rd minute, before Shola Amoebi was sent off for a second bookable offence.
Substitute Will Hoskins then sealed victory for the Championship side late on when he coolly stroked home David Lopez’s pass.
Fifteenth-placed Newcastle are currently just two points above the relegation zone in the Premier League after suffering eight defeats in their last 10 top-flight outings.
And Saturday’s loss meant that the Magpies have not won away from St James’ Park all season after 16 attempts in all competitions.
“We didn’t have enough quality players on the pitch for a Newcastle team, we are missing so many players,” Pardew said.
“Our younger players gave everything they could but it wasn’t enough and it didn’t help when we went down to 10 men.
“For us, the season we are having, we just need to get our best players back and quickly. We need to sustain ourselves in the Premier League. We want to stay there but we are in danger and we need to get our best players out on the pitch.
“If I am being honest that team is a shadow of the team we put out last season. We need to get some bigger players back, who can handle the situation of carrying the Newcastle jersey. Whether that is a signing or a case of getting some of them back fit, I don’t know.”
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news