Sobotka has five points (two goals, three assists) in the Stanley Cup Playoffs. He rejoined the Blues from the Kontinental Hockey League on April 9.
"He's had a really strong playoff for us," St. Louis coach Mike Yeo said. "He's been very effective and it's not hard to figure out why. You get into playoff hockey and to have success, you want speed, you want skill, but the level of competitiveness goes up.
"When he plays the way that he does and he gets to the hard areas, he protects the puck, he wins battles offensively, opens up time and space for other people and creates situations and opportunities for himself as well."
Stastny has one assist in the series. He missed all but the final game of the first round against the Minnesota Wild with a lower-body injury.
"Our backs are against the wall here. We have to do something," Stastny said. "I think I said that last game. We had a lot of chances and had to create a lot to score and they didn't go in. We're not lacking any confidence.
"We know something needs to happen. If you lose a couple games in a row, obviously you have to shake things up a little bit. This way you just spread it out a little bit."
The fourth line will reunite Kyle Brodziak, who was a healthy scratch in Game 4, with wings Scottie Upshall and Ryan Reaves.
"This time of year, you don't ask questions," said Brodziak, who has two assists and is minus-3 in eight playoff games. "You put in the work you need. If they don't feel your game's up to the level that it needs to be, then you've got to work on it and get it back where it needs to be. Like I said, it's tough; you want to be a part of it, but hopefully use the last few days to try to get it to the level I know I can play at."