Rodrigo's goal saw Valencia win 1-0 on the first matchday of the Champions League group stage as Barkley squandered his side's late chance to equalise from the spot at Stamford Bridge.
Liverpool will prove a big challenge for Chelsea, having won each of their first five league games, but the two sides have already faced off in the UEFA Super Cup final.
The match proved Chelsea can be competitive against the European champions as they fell on penalties after a 2-2 draw over 120 minutes in Istanbul.
"Every side is beatable on the day. It just goes down to hard work, putting extra yards in, being clinical as well and a bit of luck. The big games bring the best out of all players," Barkley told reporters.
"As you have seen in the Super Cup final and how well we performed in that game, and we can perform to those levels again on Sunday and hopefully it goes our way.
"We are joint-third [in the league on points]. We’re not doing badly. We won at the weekend, scoring goals. We have got a confident bunch of lads in the team. We have got a big game on Sunday and we are confident we can win the game."
Frank Lampard's return to west London as manager has been greeted with jubilation among the home fans. Lampard is the club's all-time leading scorer with 211 goals and won every major team honour over a 13-year spell as a player.
However, he is still searching for his first home win as manager and Barkley believes it will come sooner or later.
"That’s a weird anomaly," he added. "We are going to win home games, aren’t we? We haven’t won yet but there is a big game coming up at the weekend. Hopefully, we win that and start winning our home games."
In the Champions League, Chelsea are under more pressure having lost their opener against Valencia.
Barkley says that Chelsea are unmoved by the disappointment of Tuesday night and are instead focused on the matches to come in the Champions League.
"We have lost our first game but there are five other games. Our focus to win those five other games," he said.