Police said he was armed with a stolen gun and they had been tracking him. They blamed the violence on a small group of people.
Four officers have been placed on administrative leave.
The wounded man's name and age have not been released by police.
But the St Louis Post-Dispatch identified him as 18-year-old Tyrone Harris, having spoken to his father, the paper said.
The shooting of 18-year-old Michael Brown in Ferguson by white police officer Darren Wilson in August 2014 sparked demonstrations across the United States.
Although Mr Wilson was cleared of wrongdoing by a grand jury and by the US Department of Justice, the teenager's death fuelled a national protest movement against the use of excessive force by police officers.
A justice department investigation also found widespread racial bias in the Ferguson police force.
What happened in Ferguson in 2014?
US Dept of Justice report on Ferguson racism
Earlier on Sunday, hundreds of people stood silent for four-and-a-half minutes at the spot where Michael Brown was killed, representing the number of hours that his body lay in the street unattended.
The BBC's Aleem Maqbool, who is in Ferguson, says most people at Sunday's gathering felt little had changed since Michael Brown was shot dead a year ago.
At the end of a sombre, peaceful day of commemorations, shots were heard at about 23:15 local time on Sunday (04:15 Monday GMT) as a large crowd gathered on West Florissant Avenue,
St Louis County Police Chief Jon Belmar told reporters that after "an exchange of gunfire between two groups" the suspect, believed by police to be armed, left and encountered officers in an unmarked SUV.
He said the suspect fired on the vehicle and the plainclothes detectives returned fire from inside the van. There was then a further exchange of fire after the officers left the vehicle.
The gunmen "were criminals; they weren't protesters," he said, adding that the officers were not wearing body cameras.
Photos from the scene showed a young black man lying bloodied on the ground. He was face down and handcuffed.
President Barack Obama announced a federal programme to help pay for lapel-mounted cameras for US police to record their interactions in the wake of the nationwide protests on perceived policing injustices.
There have been a number of high profile shootings of unarmed black men in US cities in recent months.
The most recent case involved 19-year-old Christian Taylor who was shot dead by a white police officer after he was spotted on surveillance footage vandalising cars in Arlington, Texas, on Friday.

England was ranked seventh for child independence in the study of 18,000 seven- to 15-year-olds in 16 countries, by University of Westminster academics.
Freeing children to go out alone in their local area benefited their health and development, the researchers said.
Fear over traffic was the top reason for restricting freedom, they added.
The children and their parents were surveyed between 2010 and 2012 about what they were allowed to do in their local neighbourhoods without supervision.
This included:
The study said: "A large proportion of children under 11 years old in most of the countries do not have the the freedom to get about their local area.
"Even the oldest children are restricted in what they are allowed to do, at an age when many of the rights of adulthood are close to being granted, including the right to drive vehicles on the road once the test has been passed."
Overall, Finland was found to be the top-performing country on independent mobility, with Germany coming second.
According to the survey, most Finns can, without supervision:
In England, most primary school children are allowed to cross roads without supervision but only 28% to travel home from school and even fewer to go out after dark, travel on local buses or walk to places other than school.
Even at secondary school, less than 25% are allowed out alone after dark.
Ben Shaw, director of the Policy Studies Institute, said: "Obviously, we've got to protect children but part of their development is that we allow them to gain independence.
"People see the change from primary school to secondary school as the time to do it, but not having them do it earlier means there is a spike in road accidents at this age."
A man has been critically injured in Ferguson, Missouri, in an exchange of gunfire with police at a rally marking the anniversary of the killing of unarmed black teenager Michael Brown.
[NEXT_CONCEPT]
Anxious parents in England give their children less freedom to play and go outside than those in many other European countries, research suggests.