The Kilmarnock manager believes Boyd can be the difference between his side climbing the SPFL Premiership tree and languishing with the top flight's also-rans.
The Rugby Park side are on a four-game winning run against sides around them in the bottom six and, after today's match, will next be in action on Sunday against Hibernian. St Mirren visit Ayrshire on January 2, and Johnston believes Boyd, with nine goals so far this season, and his ilk will be crucial to their fortunes.
"Hearts will be desperate for a win, but when you've got the likes of Kris Boyd up front and the other attacking options we have, we are always likely to score. Having Kris is a massive advantage compared to the other sides round us. We just need to make sure defensively we keep it tight."
Kilmarnock, however, have failed to keep a clean sheet away from home, and Johnston knows that emotions will be running high following the death on Sunday of former Hearts youth player Jamie Skinner in a match for Tynecastle FC.
Johnston played for the same club as a youth and said: "I started out at Tynecastle when I was 16. My assistant here at Killie, Sandy Clark, was my reserve team manager then and went on to give me my first-team debut for Hearts. Gary Locke [the Hearts manager] and I came through the youth system together at Tynecastle too, so you can see what a successful set-up they have. But it is such a shame what happened at the weekend with the young lad. It will be an emotional day on Thursday, but what is so great about the Hearts support is that they always get behind the team, especially in circumstances like that."
Despite their lack of strength in depth, home midfielder Callum Tapping believes the next six weeks give Hearts the opportunity to turn their season into one of positives. But first they have to overturn their negative points tally. They are 14 points behind Ross County at the foot of the SPFL Premiership table and are yet to reach the zero mark, having been deducted 15 points for entering administration during the close season.
Today's match is the first of four in 10 days against three of the four teams immediately above them in the league, plus capital rivals Hibs. They also have a Scottish League Cup semi-final against Inverness Caledonian Thistle on February 2.
Tapping said: "It is a big period for us with Kilmarnock, St Mirren and Partick coming up. If we start picking up points and catching up then we will give ourselves a real chance. We know we are getting closer to where we want to be. We can reach zero points with a win today and it will be a massive boost to get to that mark."