England's first match in the World Cup will be on Monday 18th June against Tunisia, and Southgate says there are places up for grabs.
Jamie Vardy was denied by a flying Navas from point-blank range as England pressed their advantage, although Jack Butland made a good save to deny Johan Venegas after a rare Costa Rica break.
However, Welbeck also justified his inclusion in Southgate's squad by coming off the bench to seal the win 14 minutes from time as he headed home Dele Alli's cross.
"Henderson can play as a number eight, so that gives you an option, Dier can play as a centre-back...so they both have another way into the team".
One would assume right wing-back is one of them.More news: SES-12 satellite successfully launched
Real Madrid goalkeeper Navas was completely caught out moments later, though, as Rashford unleashed a powerful drive from 25 yards that dipped perfectly over him and into the top corner for his third global goal.
'We have got a good chance.
The start of the 2018 World Cup is now a week away, with the Three Lions hoping to improve on some dismal recent major tournament performances.
The resulting set-piece was met by Harry Maguire, who diverted a free looping header towards the bottom corner, but Bryan Oviedo hacked it off the line. "There are a couple of places that always as a manager you are looking at who your better players are, but then form and physical condition means it always evolves, a football team is a moving, living beast".
"I still need to get in the box a bit more to try and finish off some chances from crossing areas, so something to learn from each game".
England comes into this match unbeaten in their last nine games, including a narrow 2-1 win from Wembley over a very game Nigerian side on Saturday.