Substitute Gabriel Martinelli scored a stoppage-time winner as Brazil snatched a place in the round of 16 of the World Cup with a 2-1 win over Japan in Houston.

Carlo Ancelotti's side were stunned when Japan took the lead with a superb strike from Kaishu Sano after 29 minutes but replied when Casemiro atoned for a poor first-half performance with a fine header.

The game appeared to be heading towards extra time after a tense final period but Martinelli, sent on by Ancelotti on 66 minutes, capped the fightback after being played in by Bruno Guimarães.

It was harsh on an obstinate Japan side, who were chasing their country's first World Cup knockout win, but Brazil finished strongly after a lethargic first-half display.

Japan were measured throughout, sitting deep and allowing Brazil to control possession early on.

The South Americans found it difficult to create openings but did have an early chance as a Guimaraes shot was deflected behind and Matheus Cunha had an effort pushed wide by Zion Suzuki.

Japan's only opportunity in the opening stages came from a free-kick after Junya Ito was felled by Casemiro but Daichi Kamada fired into the wall.

Sano, booked early on after catching Vinícius Júnior late, escaped further punishment for a clumsy challenge on Cunha.

That was to prove controversial as Sano gave Japan the lead just before the half-hour.

The Mainz midfielder seized on Danilo's loose pass on halfway and powered past Casemiro before burying a low shot beyond Alisson Becker from outside the box.

Brazil were rocked and initially reduced to tame long-range efforts from Vinícius and Cunha in response, but Ancelotti's half-time adjustments prompted a change of tempo.

Guimaraes tested Suzuki with a strong header and Casemiro had an even better chance moments later but planted his header against Takehiro Tomiyasu on the line when he seemed certain to score.

Ito's clearance led to a quick Japan counter-attack but it came to nothing.

Casemiro made no mistake when he got another chance on 56 minutes, firmly heading past Suzuki at the back post from a Gabriel cross.

Japan were reeling and Vinicius almost put Brazil ahead when he weaved his way through the area and attempted to flick over Suzuki, but the keeper just managed to touch onto the post.

Japan recovered their composure and held Brazil back for long periods in a tight ending but Brazil eventually found a way through.

Five minutes of stoppage time had elapsed when Guimaraes slipped in Martinelli and he bent a shot past Suzuki.