Basel won 2-1 at Stamford Bridge in the opening game in Group E back in September, but the two teams' results have subsequently taken different trajectories.
Chelsea have won three games in a row in the competition and know avoiding defeat in Switzerland on Tuesday night will secure their spot in the last 16.
Meanwhile, Basel lost at home to Schalke before twice drawing 1-1 with Steaua Bucharest, although they still have a chance of making the next stage.
Murat Yakin's side are third in the group, one point behind Schalke, and Chilean midfielder Diaz is keen to keep Basel in the hunt ahead of a final fixture with the German club.
"For us, the key in this match is to maintain our chances in Europe until the last day," Diaz told Sky Sports. "For this, we have worked very hard on our strategy.
"If Basel can win in London, we can also beat Chelsea at home, but that is not going to be easy.
"Now, Chelsea are playing at a better level than at the time of the match at Stamford Bridge. Principally, it's in the defensive system because now it is more difficult to score a goal past Cech.
"Basel were happy with that victory, but that is in the past and now we dream of beating the Blues and continuing our dream in Europe.
"I expect a hard match, but we could surprise them."