Twelve months later, the Mariners are little more than a footnote in Lee's whirlwind of roster maneuvers, a team he pitched 13 games for between World Series runs in Philadelphia and Texas.
But as Lee lands back with the Phillies now in this week's blockbuster free-agent signing, it's worth looking at how the Mariners came out in that whole deal as well.
While the Mariners might be just a blip on Lee's career track, the flip they performed in acquiring and then trading him again seven months later to the Rangers could turn out to be a key move in the club's rebuilding efforts.
No, the Mariners couldn't convert Lee's presence into a contending role in 2010. Though he was a sterling 8-3 with a 2.34 ERA in his 13 appearances after starting the season on the disabled list, the Mariners' lack of offense led to quick elimination in the American League West, and he was swapped to Texas on July 9.
But Seattle wasn't shut out in that shuffle. From all appearances, the club seems to have come out well in the prospect swap.
After giving up youngsters Phillippe Aumont, Tyson Gillies and J.C. Ramirez to the Phillies last December, the Mariners received a more advanced return in Justin Smoak, Josh Lueke, Blake Beavan and Matthew Lawson when they sent Lee to Texas.
The Mariners did include Major League reliever Mark Lowe in the Rangers' deal, so that must be considered as well. But they got back a player in Smoak who now sits at the heart of their hopes for an improved offense, as well as a power arm in Lueke, who is projected to be a key piece in this coming season's bullpen.
"We are very pleased with the return in the trade as all four players should be contributors to our current Major League club at present and in our very near future," said Mariners general manager Jack Zduriencik.
"We view Smoak as a middle-of-the-lineup bat and Lueke as a late-inning guy. Both should be with us in 2011. Beavan is a future starting pitcher who is not that far away and who competed in Triple-A at just 21 years of age in 2010. And Matt Lawson should fit a role as a Major League contributor as well."
Beavan advanced to Triple-A Tacoma late last season and picked up a postseason victory for the Rainiers. The 2007 first-round Draft pick figures headed back to Tacoma this year for further seasoning, but provides rotation depth and a nice arm for the future.
Lawson, who just turned 25, hit .319 with an .815 OPS for Double-A West Tennessee.
On the flip side, the three Mariners prospects sent to the Phillies all struggled last season.
Aumont, Seattle's first-round Draft pick in 2007, is regarded as the prize prospect in that group. And while he's just 22 and has time to emerge, he wound up getting demoted from Double-A Reading to Class A Clearwater by the Phillies in midseason after going 1-6 with a 7.43 ERA in 11 starts.
Aumont was 2-5 with a 4.48 ERA in high Class A ball, and there are questions being raised again about whether he is more suited to a relief role, as the Mariners had projected.
Ramirez, a 22-year-old right-hander from Nicaragua, successfully made the jump from Clearwater to Reading. He was 4-3 with a 4.06 ERA in Class A ball and then 3-4 with a 5.45 ERA at Double-A, but wound up requiring surgery on a labrum tear in his hip after the season.
Gillies, also 22, ran into hamstring problems that limited him to 26 games of Double-A ball. He hit .238 with just a .619 OPS in 105 at-bats for Reading and also had an off-field issue with a drug-possession charge that was eventually dropped, but it wasn't a great year for the promising outfielder.
None of the three were ranked among the Phillies' top 10 prospects in a recent rating by Baseball America.
The Mariners, meanwhile, landed a player in Smoak who is regarded as one of the better young hitting prospects in baseball. While the 24-year-old struggled in his initial shot in Seattle, he rebounded strongly after being recalled from Tacoma in the closing weeks of the season.
In 30 games with the Mariners, he hit .239 with five home runs and 14 RBIs. But in his final 14 games after being recalled, the big lefty batted .340 with three home runs and nine RBIs in 50 at-bats.
Lueke, who just turned 26, has yet to reach the Major Leagues. But the hard-throwing right hander was 1-0 with a 2.08 ERA with a pair of saves in 17 1/3 innings with Tacoma in the closing months last year and had a strong Arizona Fall League showing as well.
Zduriencik considers Lueke and Dan Cortes as two young power arms who should bolster the Mariners' bullpen this coming year.
One other less-tangible impact of Lee's presence in Seattle was the quick pace and professionalism he displayed, which seemed to rub off on some of the young Mariners pitchers.
So while Seattle might have been just a brief stop in Lee's career, he clearly left a positive impact as well as a new group of supporters in his wake.
"We're happy for Cliff," Zduriencik said. "I'm an admirer of what he's accomplished, how he's gone about his trade and am happy he and Kristen are where they feel most comfortable playing.
"We wish things would have worked out better for us and for him in 2010. It didn't go as planned with his injury for the first month of the season and then ending in the trade to Texas. [But] in his short time here, he was fun to watch, and he has many people pulling for him and his future success. He truly is a real pro."