This will be Iran boss Carlos Queiroz's 13th World Cup match.
His teams have scored only one first-half goal - Raul Meireles for Portugal against North Korea in 2010. There have been 13 goals since - all second half.
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Iran v USA (19:00 GMT)
Not sure you'd guess either of these names for most chances created...
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Iran v USA (19:00 GMT)
BBC Two
BBC Two coverage of this game has just started... NOW.
Switch on your TV or press play near the top of this page.
USA boss sorry for Iran flag tweet
Iran v USA (19:00 GMT)
United States manager Gregg Berhalter has apologised after a modified version of Iran's flag was used in social media posts by the US national team.
Before their World Cup meeting on Tuesday, the US removed the the Islamic Republic emblem from the flag in graphics posted online, which were later deleted.
Iran's football federation complained to Fifa over the issue.
"Sometimes things are out of our control," Berhalter said on Monday.
"We're not focused on those outside things and all we can do is apologise on behalf of the players and the staff, but it's not something that we were a part of."
A father and son from England were soaking up the pre-match atmosphere around the Al Thumama Stadium earlier.
I asked who they were supporting tonight, whether they had missed out on England tickets and if this was the next best thing.
"We could have tried to go to the England match but they are basically through so this one had more riding on it. It could be brilliant!"
They have chosen to cheer on the USA, hence the shirt, because they have family living in Austin, Texas.
As I walked away I tried to think of an American who played for Villa and the first player that came to mind was goalkeeper Brad Friedel.
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Iran v USA (19:00 GMT)
BBC Sport takes a look back at the "politically charged" build-up to USA's match with Iran at the 1998 World Cup.
The US and Iran cut diplomatic relations in 1980.
Iran won that game 2-1 - but both failed to qualify from the group.
"That game sticks in my mind, it burns in my mind," said US boss Gregg Berhalter.
"What I saw from the first whistle is one team that really wanted to win the game and one that didn't want to win."
Fans keeping score
Iran v USA (19:00 GMT)
Emma Sanders
BBC Sport at Al Thumama Stadium
BBC SportCopyright: BBC Sport
Before kick-off, fans were keeping a close eye on the earlier matches in Group A where the Netherlands and Senegal secured their spots in the last 16 with wins.
Fans were gathered around large screens showing the games, with a DJ set close by and a few other bits of entertainment.
As I walked around about two hours before kick-off at the Al Thumama Stadium, there was a nice atmosphere brewing. Plenty of USA fans.
Who needs what?
Iran v USA (19:00 GMT)
The winner of this game reaches the last 16, simple as that.
A draw would be enough for Iran IF Wales don't beat England. If Iran draw and Wales win, then goal difference comes into play - and Iran probably go out.
BBC SportCopyright: BBC Sport
Team news - Sargent starts for USA
Iran v USA (19:00 GMT)
Emma Sanders
BBC Sport at Al Thumama Stadium
There is just one change to the Iran side from their 2-0 victory over Wales.
Goalkeeper Alireza Beiranvand has returned, replacing Hossein Hosseini, following an apparent concussion picked up in the defeat to England.
Live Reporting
Emlyn Begley
All times stated are UK
Post update
Iran v USA (19:00 GMT)
This will be Iran boss Carlos Queiroz's 13th World Cup match.
His teams have scored only one first-half goal - Raul Meireles for Portugal against North Korea in 2010. There have been 13 goals since - all second half.
Post update
Iran v USA (19:00 GMT)
Not sure you'd guess either of these names for most chances created...
Post update
Iran v USA (19:00 GMT)
BBC Two
BBC Two coverage of this game has just started... NOW.
Switch on your TV or press play near the top of this page.
USA boss sorry for Iran flag tweet
Iran v USA (19:00 GMT)
United States manager Gregg Berhalter has apologised after a modified version of Iran's flag was used in social media posts by the US national team.
Before their World Cup meeting on Tuesday, the US removed the the Islamic Republic emblem from the flag in graphics posted online, which were later deleted.
Iran's football federation complained to Fifa over the issue.
"Sometimes things are out of our control," Berhalter said on Monday.
"We're not focused on those outside things and all we can do is apologise on behalf of the players and the staff, but it's not something that we were a part of."
Read more here.
'This had more riding on it'
Iran v USA (19:00 GMT)
Emma Sanders
BBC Sport at Al Thumama Stadium
I found an Aston Villa fan!
A father and son from England were soaking up the pre-match atmosphere around the Al Thumama Stadium earlier.
I asked who they were supporting tonight, whether they had missed out on England tickets and if this was the next best thing.
"We could have tried to go to the England match but they are basically through so this one had more riding on it. It could be brilliant!"
They have chosen to cheer on the USA, hence the shirt, because they have family living in Austin, Texas.
As I walked away I tried to think of an American who played for Villa and the first player that came to mind was goalkeeper Brad Friedel.
Post update
Iran v USA (19:00 GMT)
BBC Sport takes a look back at the "politically charged" build-up to USA's match with Iran at the 1998 World Cup.
The US and Iran cut diplomatic relations in 1980.
Iran won that game 2-1 - but both failed to qualify from the group.
"That game sticks in my mind, it burns in my mind," said US boss Gregg Berhalter.
"What I saw from the first whistle is one team that really wanted to win the game and one that didn't want to win."
Fans keeping score
Iran v USA (19:00 GMT)
Emma Sanders
BBC Sport at Al Thumama Stadium
Before kick-off, fans were keeping a close eye on the earlier matches in Group A where the Netherlands and Senegal secured their spots in the last 16 with wins.
Fans were gathered around large screens showing the games, with a DJ set close by and a few other bits of entertainment.
As I walked around about two hours before kick-off at the Al Thumama Stadium, there was a nice atmosphere brewing. Plenty of USA fans.
Who needs what?
Iran v USA (19:00 GMT)
The winner of this game reaches the last 16, simple as that.
A draw would be enough for Iran IF Wales don't beat England. If Iran draw and Wales win, then goal difference comes into play - and Iran probably go out.
Team news - Sargent starts for USA
Iran v USA (19:00 GMT)
Emma Sanders
BBC Sport at Al Thumama Stadium
There is just one change to the Iran side from their 2-0 victory over Wales.
Goalkeeper Alireza Beiranvand has returned, replacing Hossein Hosseini, following an apparent concussion picked up in the defeat to England.
Winger Alireza Jahanbakhsh is suspended.
Iran XI: Beiranvand, Hajisaf, Mohammadi, Ezatolahi, Pouraliganji, Taremi, Gholizadeh, M Hosseini, Azmoun, Noorollahi, Rezaeian.
There are two changes to the USA team from their goalless draw with England.
Defender Walker Zimmerman and forward Haji Wright drop to the bench. In comes Celtic's Cameron Carter-Vickers and Norwich City's Josh Sargent.
Leeds midfielder Tyler Adams captains the side, with Chelsea's Christian Pulisic in attack.
USA XI: Turner, Dest, Adams, Robinson, Musah, McKennie, Pulisic, Ream, Carter-Vickers, Weah, Sargent.
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Iran v USA (19:00 GMT)
Hello and welcome to live text and TV coverage of the *other* Group B game as Iran face USA for a place in the last 16 of the World Cup.
Wales v England is this way.