Glen Johnson proved against Andrew Fonfara that he can still fight at 43 years old.

“The Road Warrior,” battling with the spirit we expect from him, gave his young opponent all he could handle for at least half the fight before fading down the stretch and losing a unanimous decision Friday in Chicago, Fonfara’s hometown.

The question was whether Johnson can still be competitive with a top-tier light heavyweight. The answer, sadly, probably is “no.”

Johnson acknowledged that notion when he announced his retirement shortly after the fight, ending what could one day be a Hall of Fame career.

The old man went out swinging. He looked strong during the first half of the fight Friday, competing with the 24-year-old from Poland on at least even terms. Johnson, a typically busy fighter, outworked Fonfara and landed the cleaner punches in the early rounds.

However, the 6-foot-2 Fonfara, doing his best work from a distance, got in his licks too and maintained his pace for 10 full rounds.

Johnson seemed to tire in the seventh or eighth round, which allowed Fonfara to break open what had appeared to be a close fight. The official scores –  99-91, 97-93 and 97-93 – were a tad too generous for the hometown boy but no one will complain too vociferously that Fonfara won.

Johnson has now lost three consecutive fights, the previous two a majority decision against Carl Froch and a shutout against Lucian Bute. He also is 4-5 in his last nine fights, with four of the five losses coming against elite opponents.

The fact that Johnson struggled against a good, but unproven opponent like Fonfara undoubtedly convinced him that enough is enough.

Johnson, who got his nickname because he fought in the hometown of his opponents so often, lost most of his biggest fights. They include setbacks against Bernard Hopkins, Antonio Tarver, Chad Dawson, Froch and Bute, among several other big-name foes.

And he failed in his first three attempts to win a major title before outpointing Clinton Woods to win the IBF light heavyweight belt in 2004. That preceded his greatest moment in boxing – a one-punch, ninth-round knockout of Roy Jones Jr. in his next fight.

Johnson soon vacated the title and would never again wear a major belt. And no one seemed to care.

The Jamaican-born resident of Miami was appreciated because of the fire with which he always fought in the ring and the grace with which he carried himself outside it. He was admired by his fellow fighters and fans alike.

And the result of Friday’s fight certainly won’t change that.

For Fonfara, it was a big night. The Pole was 11-0 since he was stopped in two rounds by Derrick Findley in 2008 – including knockouts in his last nine fights – but had never faced anyone with the pedigree of Johnson.

This was a significant test that would determine whether Fonfara has the ability to take the next step in his career. He passed the test.

Not only did he win, he was fairly impressive in doing it. He took Johnson’s best shots and was never fazed. And, perhaps feeding off the home crowd, he seemed to get better and better as the fight progressed.

Yes, Johnson was at the end of his career. However, again, even this version of Johnson could beat all but the best light heavyweights. One must say that if Fonfara isn’t among that group, he’s not far from it.

He’ll also be the answer to a trivia question: Who was the last man to fight Glen Johnson?