The 23-year old Costa Rican has deputised brilliantly for Leighton Baines at left-back since the England ace has been sidelined with a toe injury.
Since late November, Oviedo has slotted in positively for four starts and Jagielka feels he has been handy in an otherwise settled Toffees defence.
"Obviously Brian's come in for the last few weeks, but other than that pretty much the back five has stayed as it is, and we've been together for a while now," said Jagielka who has seen Everton let in just 15 goals in 16 matches so far.
"So it's been pretty simple for the manager to keep us going in a direction that obviously David Moyes left and managed to tweak things going forward.
"We're delighted to keep the clean sheets, but it's all about winning the games at the moment."
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