Jermaine Defoe was regularly used as a winger when Sam Allardyce first took over at Sunderland.
Allardyce appeared to have doubts over utilising Defoe as a lone striker when he first took charge of the Black Cats, and the veteran forward was often forced to play in a wing position.
However, Defoe has now established his place as Sunderland’s main striker - and Jenas believes he will be the difference between relegation and survival.
"Sam Allardyce actually messed him about a bit when he first took over at the Stadium of Light, playing him out wide, and there was even talk that he might leave. But it's no surprise that as soon as Big Sam started playing him up front, the goals began to flow," Jenas wrote in his column for Yahoo. "They always will with Defoe. For a club like Sunderland, that kind of player is the difference between staying up and going down.
"Sunderland have a striker in Jermain Defoe who is guaranteed to get you goals. I played alongside Defoe for many years, for club and country, and he's one of the best strikers I've played with. Alan Shearer would be my number one, but in terms of out-and-out finishing Defoe is next on my list. He's absolutely relentless, deadly."
Defoe has been a revelation this season, as he has enjoyed his most productive scoring campaign in England for some time.
The 33-year-old has rolled back the years, and he netted his 15th goal of the campaign in the Tyne-Wear derby last weekend.
Defoe lashed in from close-range to put Sunderland in front, but his side were pegged back when Aleksandar Mitrovic struck a late equaliser.
The draw has left Sunderland in 18th place in the Premier League table, with time running out for them to climb out of trouble.
Allardyce’s men’s next match comes against West Bromwich Albion after the international break.