"To be honest, I still feel like I weaseled my way into the big leagues," Romo said. "Everything that's happened, I feel very fortunate.
"It's a very proud moment. I never saw myself making an All-Star team. Now that it's happening, I'm very proud, and I'm proud that my teammates congratulated me and let me know that I'm deserving. To know that they feel I'm deserving, that's what's most gratifying about it."
Romo and Melancon are stepping in for Pirates starter Jeff Locke and Nationals starter Jordan Zimmermann, both of whom are resting minor injuries. Mujica steps in for teammate Adam Wainwright, who started Sunday night's game against the Cubs.
Tillman is the substitute for the Tigers' Justin Verlander, who started against the Tigers on Sunday afternoon and therefore could not pitch on Tuesday. Holland was named to replace Mariners right-hander Hisashi Iwakuma, who started Sunday, and Balfour, coincidentally, replaces teammate Bartolo Colon on the AL roster, with Colon unavailable to pitch Tuesday after starting Sunday's game against the Red Sox.
McCann was added to the roster to replace NL Final Vote winner Freddie Freeman, who injured his thumb on Saturday, giving the Senior Circuit an extra catcher with the Cardinals' Yadier Molina injured.
With the addition of five first-time All-Stars, this year's rosters feature a record 38 newcomers, surpassing the total of 35 from the 2011 game at Arizona.
Romo has racked up 21 saves and posted a 2.86 ERA for All-Star skipper Bruce Bochy. Last year, Romo recorded the final out in nine of the Giants' 11 postseason victories, as the club won its second World Series championship in three years.
Melancon gives the Pirates five All-Stars, the club's most since 1972, when a Bucs contingent including Hall of Famers Roberto Clemente and Willie Stargell made the trip to Atlanta. The 28-year-old has excelled as a setup man for fellow All-Star Jason Grilli. Melancon owns an NL-best 0.81 ERA, holding batters to a .193 average and striking out 46 in 44 1/3 innings.
"He's been almost automatic in the eighth inning for us," said Pittsburgh general manager Neal Huntington, who acquired Melancon in a trade with the Red Sox this offseason.
McCann has rebounded well from a tough 2012 and now is an All-Star for the seventh time despite beginning the season on the disabled list. Since debuting on May 6, he has hit .291 with 12 home runs, 32 RBIs and a .910 OPS.
"Freddie's carried us," McCann said. "It's unfortunate that he won't be able to play in the game. I'm happy to be going in his place. I'm glad someone in this clubhouse got to go in his place, but I feel bad for him that he won't be able to enjoy it on the field."
With Tillman's inclusion, the Orioles now have five All-Stars, their most since Hall of Famers Cal Ripken Jr. and Roberto Alomar led a group of five to Cleveland in 1997. Tillman is 11-3 this season, with a 3.95 ERA and 89 strikeouts in 111 2/3 innings.
"It's huge. We were all just as excited as he was when we found out today," said Baltimore first baseman Chris Davis, another All-Star. "The guy's worked hard all year. He's been a guy that we really depend on, a guy that's really been a horse for us."
Holland will join two teammates, outfielder Alex Gordon and catcher Salvador Perez, in New York. In his first season as a closer, he has racked up 22 saves, with a 1.80 ERA and a whopping 60 strikeouts in 35 innings.
"It's exciting," Holland said. "I thought a lot about it leading up to it and I didn't get in but I was so happy for Salvy and Gordo that it was kind of easy to move on from."
In his 10th big league season out of Australia, Balfour is an All-Star for the first time.
"Balf deserves to be an All-Star as well," manager Bob Melvin said, "and thank goodness he is."
The 35-year-old has notched 25 saves, with a streak of 43 consecutive conversions going back to last year. His outing on Sunday against the Red Sox dropped his ERA to 1.63.
"I'm relieved. It's definitely a great honor to be going," Balfour said. "It's one of those things, each and every year, you'd like to be on the team. It hasn't worked out that way. I feel like I've had some good years, but things have to go right and go your way sometimes, and it's just an honor now to be named to it, and I'm very happy to cross it off the list."
The final phase of All-Star Game voting will again have fans participating in the official voting for the Ted Williams All-Star Game Most Valuable Player Award presented by Chevrolet. During the Midsummer Classic, fans will vote exclusively online at MLB.com via the 2013 All-Star Game MLB.com MVP Vote, and their voice will represent 20 percent of the official vote determining the recipient of the Arch Ward Trophy.
The 2013 All-Star Game will be played at Citi Field on Tuesday. Come to MLB.com for extensive online coverage of the All-Star Week festivities.
The 84th All-Star Game will be televised nationally by FOX Sports, in Canada by Rogers Sportsnet and RDS, and worldwide by partners in more than 200 countries via MLB International's independent feed. ESPN Radio and ESPN Radio Deportes will provide national radio coverage of the All-Star Game. MLB Network and SiriusXM also will also provide comprehensive All-Star Week coverage. For more information, please visit allstargame.com.