Then, the Angels right-hander was told his start would also coincide with Jackie Robinson Day.
"What?!" Williams said, his eyes widening as he rocked back in his chair and exhaled violently. "I didn't even know that. Oh my God. I always wanted to do that! I always wanted to wear a No. 42 jersey and never wore one."
Well, not in the big leagues, at least.
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The No. 42 has actually been indicative of the topsy-turvy path Williams' career has taken since he was a first-round Draft pick of the Giants in 1999. The last time Williams was in the Majors for the first month of a season, Major League Baseball asked teams to designate just one player to don Robinson's retired number. That was back in 2007, when he was with the Nationals; Dmitri Young wore it that year.
But Williams did wear the No. 42 twice while trying to find himself through Winter League stints in Puerto Rico and Venezuela. He wanted to while pitching in Taiwan last year, but somebody already took it.
"I always wanted to wear it, because it's very significant to me," said Williams, a Hawaii native of African-American descent. "It was instilled in me when I was younger. It's always going to be in my heart, always going to be in my mind, to go out there and do my best with that number."
But to Williams, Sunday's start is about a lot more than the celebration of baseball's most revolutionary figure.
As the 30-year-old Williams said, it's about "just proving to doubters that didn't think I was going to come back, to tell them, 'Hey, I came back, and I'm here to stay.'"
Williams will admit he didn't have good work ethic early in his career, while posting a 3.92 ERA and averaging 21 starts per season from 2003-05. That led to him spending most of the '06 season in the Cubs' Minor League system, having to sign a Minor League contract for '07, being released by the Nats in August of that year, starting the '08 season in independent ball before pitching in the Dodgers' system, spending almost the entire '09 season with the Athletics' Triple-A affiliate and playing for the Taiwanese Uni-President Lions in 2010.
Last year, the Angels saw Williams pitch for the Lancaster Barnstormers of the Atlantic League -- representing his second independent-ball team -- and figured they'd give him a shot.
Now -- after posting a 3.68 ERA in 44 big league innings down the stretch, and fully recovering from a strained left hamstring that knocked him out for most of Spring Training -- Williams is back, starting a season on a big league team and taking the ball on what he believes is the most important day of the season.
Williams lost a lot of years due to things he believes he could've controlled.
He knows he can't get them back, though.
"What I did, I did, and all I can do is go forward," Williams said. "I can't go backwards. I can't do what I did before. It's not in me anymore. It's all about maturing. Maturity was a big factor for me. You have to learn how to mature in this game. If you don't know how to mature, you probably shouldn't be playing."
Williams has one other hurdle to conquer: The presence of ESPN cameras.
Williams gave up just one run in eight frames under such a spotlight against the Mariners on Sept. 7 last season, but still prevalent in his mind is Game 4 of the 2003 National League Division Series as a member of the Giants against the Marlins, who scored three runs and chased the righty after only two innings.
"I had other bad ones [on ESPN], too," Williams said. "I just don't want to remember them."
How much sleep has Williams received heading into this next one?
"Not that much," he admitted.
"Making my first start here, first start against the Yankees, 42 -- I mean, just thinking about it is like, 'Wow, everything's being thrown at me.' Hopefully, everything will turn out good and I just don't think about that while I'm out there."
Tough not to.
Alden Gonzalez is a reporter for MLB.com. Read his columns and his blog, Gonzo and "The Show", and follow him on Twitter @Alden_Gonzalez. This story was not subject to the approval of Major League Baseball or its clubs.