Western travel to local rivals Clydesdale, who are fourth in the table after losing 4-2 at Grange last Saturday.
Johnston, who was stand-in captain against Clydesdale, said his men started well last Saturday, going 2-0 up, but the opposition pressed
“We did not react to that,” he said.“They got two goals and we took our eye off it in the second quarter."
However, Grange believed that by moving forward on the counter they could hurt the opposition and so it proved.
The Edinburgh club scored two quick goals, one after a darting, cross-field run by rising star Fraser Heigh, the club's top marksman so far this term.
Johnston explained: “It was the same the previous week, when we scored one we scored another straight away.”
Duncan Riddell stood out, the Scottish international running midfield for Grange, as did Heigh in flashes.
Johnston said: “Duncan is always class. The team gives them the license to go forward and do what they want to do. There are other strong dribblers, strong players in the team."
Looking forward to the game against Dunfermline at Fettes College (noon), the stand-in skipper said Grange will not taking them for granted.
He added: “We have played them twice and in the first game we took them for granted. We weren't really there.
“In the second game we went back to their pitch and were much better, scoring eight goals."
He added: “We can't focus on Western. It is about us. If we lose then we are out of it so it is up to us to keep winning.”
Saturday: Watsonians v Edinburgh, University (no time given, Peffermill); Kelburne v Hillhead (11.45, Glasgow National Hockey Centre); Grange v Dunfermline Carnegie (noon, Fettes College); Dundee Wanderers v Inverleith (13.30, Dalnacraig); Clydesdale v Westrn (15.00, Titwood); Uddingston v Grove Menzieshill (15.00, Uddingston Cricket and Sports Club).