The Proteas have have had a tough tour Down Under having already surrendered the three-match series with a game to spare.
The home side won the first Test in Brisbane by six wickets in a match that only lasted two days and then sailed to an innings-and-182-run victory in the Boxing Day Test in Melbourne.
Jansen has been one of the few visiting players to come away with any credit in the last two games, taking big wickets and scoring his maiden half-century at the MCG.
The lanky seamer told reporters om Monday: "I know everyone goes out there to give their best, but at the end of the day it's about trying to figure out what we can do as a team or individuals to really influence the game in a defining way.
"Whether it's taking five blows to the body while batting or bowling 7 or 8 overs on the trot, it's those things that matter. It's about recognising the moment and doing whatever you can within your power to influence or help the team.
"You can say all these nice things about 150-plus partnerships or guys scoring double centuries, but it's not always a case where a team scores 500 runs and then win the game.
"Test cricket is sometimes like the first Test, where a partnership of 80 wins you the game. My focus is on identifying those type of moments and capitalising on them."
The two defeats in Australia has seen the Proteas slip down to fourth in the World Test Championship (WTC) table with their hopes of finishing in the top two and a place in the final now a meek possibility.
South Africa only have three Tests remaining to influence the final outcome, the match in Sydney and two games at home against West Indies starting next month.
When asked if they have something to play for, Jansen said: "Ja, definitely [there's something to play for]. I think we have three Test matches left [two against West Indies in February/March] until the final, so obviously we want to win all three to give ourselves the best chance possible to get into the final.
"So, it's not like we're going into this game just thinking, 'Ok, it's just another game, we can just cruise through it,' or whatever. There's still a goal, there's still a purpose going into this next Test."