The arrival of the Celtics and Lakers in the NBA finals sparked a wave of nostalgia about the legendary rivalry between the franchises. Most of the history pieces revolved, fittingly, about the megawatt duels between the Larry Bird Celtics and the Magic Johnson Lakers in the 1980s and early ‘90s.

But maybe because it’s summer, and baseball season, I decided to focus on two players from the 1959 finals in which the Celtics swept the Lakers, four games to zero. At the time, you see, the Celtics’ Gene Conley also was a major-league baseball pitcher and the Lakers’ Steve Hamilton was about to become one.

In fact, when the Celtics clinched the title with a 118-113 road victory on April 9, it made Conley the only player in sports history to be a member of the reigning NBA champs and the reigning World Series champs at the same time. He was a pitcher for the Milwaukee Braves, who defeated the New York Yankees in the 1958 World Series.

Here in the age of specialization, overlap, and prolonged playoffs, it’s almost inconceivable that a player could play two professional sports at the same time. The last to try were Bo Jackson and Deion Sanders, who played simultaneously in both the major leagues and the NFL in the 1980s and early ‘90s.

But baseball and the NBA at the same time? Heck, when baseball players report for spring training in February the NBA is just about reaching the halfway point of the regular season. And when NBA players report for training camp in September, the big-league teams aren’t even into the playoffs yet.

Hamilton, a 6-foot-6 lefthander from Morehead State University in Kentucky, didn’t try to play both sports simultaneously. After graduating from college, where he was an honorable-mention All-American forward, he served in the Armed Forces for a couple of years, then joined the Lakers in 1958.

At the time, of course, the Lakers were located in Minneapolis, their home since they joined the NBA in 1948. Only Vern Mikkelsen was left from the great Lakers teams, led by George Mikan, that won NBA titles in 1949, ’50, ’52, ’53 and ’54.

Playing in 67 games, Hamilton came off the deep end of the Lakers’ bench and averaged 4.4 points in 1958-’59. He played for the Lakers one more year, averaging 5.1 points for a 1959-’60 team that got beat by the St. Louis Hawks in the division finals, but decided to try baseball instead of moving with the Lakers to Los Angeles.

From 1961-’72, pitching mostly in relief, Hamilton had a 40-31 record with 42 saves and a 3.05 earned-run average. He came up with Cleveland in 1961 and was traded to the Washington Senators, where he spent a year and a half before being traded to the Yankees in the summer of 1963.

He pitched an inning in the Yankees’ 1963 World Series loss to the Los Angeles Dodgers, joining Conley as the only men to ever appear in both the World Series and the NBA finals. A year later, he pitched two innings in the Yankees’ World Series loss to the St. Louis Cardinals.

On Aug. 5, 1966, Hamilton got a rare start and pitched a complete-game shutout against the Cleveland Indians, allowing only five hits. Later in his career, he became known for throwing the “Folly Floater,” a high, slow pitch that brought to mind the “Eephus Ball” thrown by Rip Sewell decades earlier.

On June 24, 1970, in the first game of a double-header against Cleveland, Hamilton threw a “Folly Floater” to slugger Tony Horton, who fouled it out of play. Horton motioned Hamilton to throw him another and Hamilton obliged. Whiffing ingloriously, Horton crawled back to the dugout on all fours.

Conley’s career in both sports was far more spectacular.

As a high-school senior in Richland, Wash., Conley was a good enough basketball prospect to attract scholarship offers from big-time coaches such as Kentucky’s Adolph Rupp, Oregon State’s Slats Gill, and Oklahoma A&M’s Henry Iba. But he turned them down in favor of Washington State. As a sophomore,  Conley starred in basketball and pitched the Cougars into the College World Series, where they finished second.

Instead of returning for his junior year, Conley signed a minor-league baseball contract with the Boston Braves, who sent him to play in the Eastern League. It was there, during the summer of 1952, that he faced a hitter named Bill Sharman, who subsequently recommended him as a basketball player to his coach with the Boston Celtics, Red Auerbach.

“He (Sharman) went to Red and told him I could play basketball,” Conley said in a 2006 interview. “He thought I could come in and help the team. Red trusted Bill’s opinion. Back then, that’s how a lot of the basketball decisions were made because you didn’t have all the technology and all the scouts that teams have today. Red hadn’t seen me play, but he knew Bill. And that was good enough for him.”

The hapless Braves brought up Conley for three games late in the 1952 season, and Auerbach made a two-sport player in the same city by signing him to a Celtics contract. He played 39 games in the 1952-’53 season, averaging 2.3 points for a team that included Sharman, Bob Cousy, and “Easy Ed” Macauley.

The Braves cracked down on Conley and forced him to make a choice. He picked baseball, and, after spending the entire 1953 season in the minors, joined the Braves in Milwaukee, their new home, in 1954. He went 14-9, made the All-Star team, and was second in the Rookie of the Year balloting.

Basketball all but forgotten, Conley became an important part of a great Braves’ staff led by Warren Spahn, Lew Burdette, and Bob Buhl. He went 9-9 for the pennant-winning 1957 team and appeared in one game in the World Series, which the Braves lost to the Yankees.

Due to an arm injury, he struggled in 1958, finishing with an 0-6 record and not even getting an appearance in the Braves’ World Series win over the Yankees. After that season, he defied Braves’ management and joined the Celtics, who needed a backup for Russell.

On March 31, 1959, while the Celtics were rolling toward the NBA championship, the Braves traded Conley, along with infielders Joe Koppe and Harry Hanebrink, to the Philadelphia Phillies for catcher Stan Lopata, shortstop Ted Kazanski, and infielder Johnny O’Brien (who, along with twin brother Eddie, had been hoops stars for Seattle in the early 1950s).

Although Phillies management also didn’t want Conley to play basketball, they grudgingly let him do it. He went 12-7 for the Phillies in 1959, then joined the Celtics in time to be part of a second straight championship team. He then reported to the Phillies for spring training, but slumped to an 8-14 record that inspired the Phillies to trade him to the Boston Red Sox.

For the second time in his career, Conley belonged to two Boston pro sports franchises.

With Conley again playing a key backup role, the Celtics won their third straight NBA title in 1961. Only nine days later, he pitched the Red Sox to a victory, earning him a special niche in the hearts of Boston fans. He finished that season, the first after Ted Williams’ retirement, with an 11-14 record.

Left unprotected in the NBA expansion draft, Conley was picked by the Chicago Bulls. But rather than report to his new team, Conley decided to give up basketball and concentrate on baseball. He won a career-high 15 games for the 1962, against 14 losses, despite being forced to admit publicly that he had been plagued by problems with alcohol for years.

After the ’62 baseball season, Conley returned to basketball, signing with the New York Knicks, and averaged a career-high 9.0 over 70 games in 1962-’63. But that was to be his last hurrah. He quit baseball during the 1963 season, and, after one more brief fling with the Knicks, retired from basketball at the end of the year.

Conley and Hamilton probably were on the floor together a few times during the 1959 NBA finals, the only time they were to cross paths in their remarkable careers. You can bet all the NBA’s pension money that no athlete ever again will reach the championship event in two major pro team sports.