Buttler's blistering 80 not out was central to England's innings and 55-run win over Pakistan inside three days at Headingley on Sunday that saw them end a two-match series all square at 1-1.
Having played himself in, Buttler accelerated in style on Sunday during an innings where he faced 101 balls in total, including 11 fours and two sixes.
Buttler was just five runs shy of equalling his Test-best score of 85, made on debut against India at Southampton in 2014, when last man James Anderson was dismissed.
Smith raised eyebrows by recalling talented ball-striker Buttler, who prior to the Pakistan series had last played Test cricket some 18 months ago, purely on the basis of his form in the Twenty20 IPL.
The 27-year-old Buttler hit five successive fifties for the Rajasthan Royals, culminating with two unbeaten 90s.
There were doubts though as to whether the white-ball form of Buttler, who has made 170 appearances in international limited overs cricket, would carry over into the Test-match arena.
But Buttler, given the freedom to attack as a specialist number seven, made 67 in England's nine-wicket defeat by Pakistan in the first Test at Lord's before starring in Leeds.
"There were lots of unknowns coming into this series so it’s especially pleasing to have put in some decent performances and especially here to be part of a winning side," Buttler said.
Buttler's 20-match Test career has often been overshadowed by the question of whether he should keep wicket -- Jonny Bairstow is now England's red-ball gloveman -- as he does in one-day cricket.
But asked if he had proven to himself he could succeed as a Test batsman, Buttler replied: "I think so.
"Over the last couple of years I've had some great experiences all round the world in different competitions," added the batsman, who has also played in Australian cricket's Twenty20 'Big Bash'.
"That's really helped. Coming into the series with someone (Smith) putting so much faith in me as a real wildcard pick gave me a hell of a lot of confidence, For someone to say 'I’m backing you, you're good enough’.
"I arrived confident having had a great few weeks in India, so I felt in a really good place and wanted to continue that and wanted to play the situations in front of me."
Buttler though could find himself in trouble with the International Cricket Council after television cameras highlighted the words "fuck it" written on the top of his bat handle.
All such "personal messages" have to be approved by the ICC -- something highly unlikely to have happened in Buttler's case -- before they can be displayed by a player.
Now it will be up to former New Zealand captain Jeff Crowe, the match referee at Headingley, to decide whether Buttler should face action for a breach of the ICC's clothing and equipment rules.
First Published: June 4, 2018, 5:59 PM IST